text: /*
   * kernel/workqueue.c - generic async execution with shared worker pool
   *
   * Copyright (C) 2002		Ingo Molnar
   *
   *   Derived from the taskqueue/keventd code by:
   *     David Woodhouse <dwmw2@infradead.org>
   *     Andrew Morton
   *     Kai Petzke <wpp@marie.physik.tu-berlin.de>
   *     Theodore Ts'o <tytso@mit.edu>
   *
   * Made to use alloc_percpu by Christoph Lameter.
   *
   * Copyright (C) 2010		SUSE Linux Products GmbH
   * Copyright (C) 2010		Tejun Heo <tj@kernel.org>
   *
   * This is the generic async execution mechanism.  Work items as are
   * executed in process context.  The worker pool is shared and
   * automatically managed.  There are two worker pools for each CPU (one for
   * normal work items and the other for high priority ones) and some extra
   * pools for workqueues which are not bound to any specific CPU - the
   * number of these backing pools is dynamic.
   *
   * Please read Documentation/workqueue.txt for details.
   */
  
  #include <linux/export.h>
  #include <linux/kernel.h>
  #include <linux/sched.h>
  #include <linux/init.h>
  #include <linux/signal.h>
  #include <linux/completion.h>
  #include <linux/workqueue.h>
  #include <linux/slab.h>
  #include <linux/cpu.h>
  #include <linux/notifier.h>
  #include <linux/kthread.h>
  #include <linux/hardirq.h>
  #include <linux/mempolicy.h>
  #include <linux/freezer.h>
  #include <linux/kallsyms.h>
  #include <linux/debug_locks.h>
  #include <linux/lockdep.h>
  #include <linux/idr.h>
  #include <linux/jhash.h>
  #include <linux/hashtable.h>
  #include <linux/rculist.h>
  #include <linux/nodemask.h>
  #include <linux/moduleparam.h>
  #include <linux/uaccess.h>
  
  #include "workqueue_internal.h"
  
  enum {
  	/*
  	 * worker_pool flags
  	 *
  	 * A bound pool is either associated or disassociated with its CPU.
  	 * While associated (!DISASSOCIATED), all workers are bound to the
  	 * CPU and none has %WORKER_UNBOUND set and concurrency management
  	 * is in effect.
  	 *
  	 * While DISASSOCIATED, the cpu may be offline and all workers have
  	 * %WORKER_UNBOUND set and concurrency management disabled, and may
  	 * be executing on any CPU.  The pool behaves as an unbound one.
  	 *
  	 * Note that DISASSOCIATED should be flipped only while holding
  	 * attach_mutex to avoid changing binding state while
  	 * worker_attach_to_pool() is in progress.
  	 */
  	POOL_DISASSOCIATED	= 1 << 2,	/* cpu can't serve workers */
  
  	/* worker flags */
  	WORKER_DIE		= 1 << 1,	/* die die die */
  	WORKER_IDLE		= 1 << 2,	/* is idle */
  	WORKER_PREP		= 1 << 3,	/* preparing to run works */
  	WORKER_CPU_INTENSIVE	= 1 << 6,	/* cpu intensive */
  	WORKER_UNBOUND		= 1 << 7,	/* worker is unbound */
  	WORKER_REBOUND		= 1 << 8,	/* worker was rebound */
  
  	WORKER_NOT_RUNNING	= WORKER_PREP | WORKER_CPU_INTENSIVE |
  				  WORKER_UNBOUND | WORKER_REBOUND,
  
  	NR_STD_WORKER_POOLS	= 2,		/* # standard pools per cpu */
  
  	UNBOUND_POOL_HASH_ORDER	= 6,		/* hashed by pool->attrs */
  	BUSY_WORKER_HASH_ORDER	= 6,		/* 64 pointers */
  
  	MAX_IDLE_WORKERS_RATIO	= 4,		/* 1/4 of busy can be idle */
  	IDLE_WORKER_TIMEOUT	= 300 * HZ,	/* keep idle ones for 5 mins */
  
  	MAYDAY_INITIAL_TIMEOUT  = HZ / 100 >= 2 ? HZ / 100 : 2,
  						/* call for help after 10ms
  						   (min two ticks) */
  	MAYDAY_INTERVAL		= HZ / 10,	/* and then every 100ms */
  	CREATE_COOLDOWN		= HZ,		/* time to breath after fail */
  
  	/*
  	 * Rescue workers are used only on emergencies and shared by
  	 * all cpus.  Give MIN_NICE.
  	 */
  	RESCUER_NICE_LEVEL	= MIN_NICE,
  	HIGHPRI_NICE_LEVEL	= MIN_NICE,
  
  	WQ_NAME_LEN		= 24,
  };
  
  /*
   * Structure fields follow one of the following exclusion rules.
   *
   * I: Modifiable by initialization/destruction paths and read-only for
   *    everyone else.
   *
   * P: Preemption protected.  Disabling preemption is enough and should
   *    only be modified and accessed from the local cpu.
   *
   * L: pool->lock protected.  Access with pool->lock held.
   *
   * X: During normal operation, modification requires pool->lock and should
   *    be done only from local cpu.  Either disabling preemption on local
   *    cpu or grabbing pool->lock is enough for read access.  If
   *    POOL_DISASSOCIATED is set, it's identical to L.
   *
   * A: pool->attach_mutex protected.
   *
   * PL: wq_pool_mutex protected.
   *
   * PR: wq_pool_mutex protected for writes.  Sched-RCU protected for reads.
   *
   * WQ: wq->mutex protected.
   *
   * WR: wq->mutex protected for writes.  Sched-RCU protected for reads.
   *
   * MD: wq_mayday_lock protected.
   */
  
  /* struct worker is defined in workqueue_internal.h */
  
  struct worker_pool {
  	spinlock_t		lock;		/* the pool lock */
  	int			cpu;		/* I: the associated cpu */
  	int			node;		/* I: the associated node ID */
  	int			id;		/* I: pool ID */
  	unsigned int		flags;		/* X: flags */
  
  	struct list_head	worklist;	/* L: list of pending works */
  	int			nr_workers;	/* L: total number of workers */
  
  	/* nr_idle includes the ones off idle_list for rebinding */
  	int			nr_idle;	/* L: currently idle ones */
  
  	struct list_head	idle_list;	/* X: list of idle workers */
  	struct timer_list	idle_timer;	/* L: worker idle timeout */
  	struct timer_list	mayday_timer;	/* L: SOS timer for workers */
  
  	/* a workers is either on busy_hash or idle_list, or the manager */
  	DECLARE_HASHTABLE(busy_hash, BUSY_WORKER_HASH_ORDER);
  						/* L: hash of busy workers */
  
  	/* see manage_workers() for details on the two manager mutexes */
  	struct mutex		manager_arb;	/* manager arbitration */
  	struct mutex		attach_mutex;	/* attach/detach exclusion */
  	struct list_head	workers;	/* A: attached workers */
  	struct completion	*detach_completion; /* all workers detached */
  
  	struct ida		worker_ida;	/* worker IDs for task name */
  
  	struct workqueue_attrs	*attrs;		/* I: worker attributes */
  	struct hlist_node	hash_node;	/* PL: unbound_pool_hash node */
  	int			refcnt;		/* PL: refcnt for unbound pools */
  
  	/*
  	 * The current concurrency level.  As it's likely to be accessed
  	 * from other CPUs during try_to_wake_up(), put it in a separate
  	 * cacheline.
  	 */
  	atomic_t		nr_running ____cacheline_aligned_in_smp;
  
  	/*
  	 * Destruction of pool is sched-RCU protected to allow dereferences
  	 * from get_work_pool().
  	 */
  	struct rcu_head		rcu;
  } ____cacheline_aligned_in_smp;
  
  /*
   * The per-pool workqueue.  While queued, the lower WORK_STRUCT_FLAG_BITS
   * of work_struct->data are used for flags and the remaining high bits
   * point to the pwq; thus, pwqs need to be aligned at two's power of the
   * number of flag bits.
   */
  struct pool_workqueue {
  	struct worker_pool	*pool;		/* I: the associated pool */
  	struct workqueue_struct *wq;		/* I: the owning workqueue */
  	int			work_color;	/* L: current color */
  	int			flush_color;	/* L: flushing color */
  	int			refcnt;		/* L: reference count */
  	int			nr_in_flight[WORK_NR_COLORS];
  						/* L: nr of in_flight works */
  	int			nr_active;	/* L: nr of active works */
  	int			max_active;	/* L: max active works */
  	struct list_head	delayed_works;	/* L: delayed works */
  	struct list_head	pwqs_node;	/* WR: node on wq->pwqs */
  	struct list_head	mayday_node;	/* MD: node on wq->maydays */
  
  	/*
  	 * Release of unbound pwq is punted to system_wq.  See put_pwq()
  	 * and pwq_unbound_release_workfn() for details.  pool_workqueue
  	 * itself is also sched-RCU protected so that the first pwq can be
  	 * determined without grabbing wq->mutex.
  	 */
  	struct work_struct	unbound_release_work;
  	struct rcu_head		rcu;
  } __aligned(1 << WORK_STRUCT_FLAG_BITS);
  
  /*
   * Structure used to wait for workqueue flush.
   */
  struct wq_flusher {
  	struct list_head	list;		/* WQ: list of flushers */
  	int			flush_color;	/* WQ: flush color waiting for */
  	struct completion	done;		/* flush completion */
  };
  
  struct wq_device;
  
  /*
   * The externally visible workqueue.  It relays the issued work items to
   * the appropriate worker_pool through its pool_workqueues.
   */
  struct workqueue_struct {
  	struct list_head	pwqs;		/* WR: all pwqs of this wq */
  	struct list_head	list;		/* PL: list of all workqueues */
  
  	struct mutex		mutex;		/* protects this wq */
  	int			work_color;	/* WQ: current work color */
  	int			flush_color;	/* WQ: current flush color */
  	atomic_t		nr_pwqs_to_flush; /* flush in progress */
  	struct wq_flusher	*first_flusher;	/* WQ: first flusher */
  	struct list_head	flusher_queue;	/* WQ: flush waiters */
  	struct list_head	flusher_overflow; /* WQ: flush overflow list */
  
  	struct list_head	maydays;	/* MD: pwqs requesting rescue */
  	struct worker		*rescuer;	/* I: rescue worker */
  
  	int			nr_drainers;	/* WQ: drain in progress */
  	int			saved_max_active; /* WQ: saved pwq max_active */
  
  	struct workqueue_attrs	*unbound_attrs;	/* WQ: only for unbound wqs */
  	struct pool_workqueue	*dfl_pwq;	/* WQ: only for unbound wqs */
  
  #ifdef CONFIG_SYSFS
  	struct wq_device	*wq_dev;	/* I: for sysfs interface */
  #endif
  #ifdef CONFIG_LOCKDEP
  	struct lockdep_map	lockdep_map;
  #endif
  	char			name[WQ_NAME_LEN]; /* I: workqueue name */
  
  	/* hot fields used during command issue, aligned to cacheline */
  	unsigned int		flags ____cacheline_aligned; /* WQ: WQ_* flags */
  	struct pool_workqueue __percpu *cpu_pwqs; /* I: per-cpu pwqs */
  	struct pool_workqueue __rcu *numa_pwq_tbl[]; /* FR: unbound pwqs indexed by node */
  };
  
  static struct kmem_cache *pwq_cache;
  
  static int wq_numa_tbl_len;		/* highest possible NUMA node id + 1 */
  static cpumask_var_t *wq_numa_possible_cpumask;
  					/* possible CPUs of each node */
  
  static bool wq_disable_numa;
  module_param_named(disable_numa, wq_disable_numa, bool, 0444);
  
  /* see the comment above the definition of WQ_POWER_EFFICIENT */
  #ifdef CONFIG_WQ_POWER_EFFICIENT_DEFAULT
  static bool wq_power_efficient = true;
  #else
  static bool wq_power_efficient;
  #endif
  
  module_param_named(power_efficient, wq_power_efficient, bool, 0444);
  
  static bool wq_numa_enabled;		/* unbound NUMA affinity enabled */
  
  /* buf for wq_update_unbound_numa_attrs(), protected by CPU hotplug exclusion */
  static struct workqueue_attrs *wq_update_unbound_numa_attrs_buf;
  
  static DEFINE_MUTEX(wq_pool_mutex);	/* protects pools and workqueues list */
  static DEFINE_SPINLOCK(wq_mayday_lock);	/* protects wq->maydays list */
  
  static LIST_HEAD(workqueues);		/* PL: list of all workqueues */
  static bool workqueue_freezing;		/* PL: have wqs started freezing? */
  
  /* the per-cpu worker pools */
  static DEFINE_PER_CPU_SHARED_ALIGNED(struct worker_pool [NR_STD_WORKER_POOLS],
  				     cpu_worker_pools);
  
  static DEFINE_IDR(worker_pool_idr);	/* PR: idr of all pools */
  
  /* PL: hash of all unbound pools keyed by pool->attrs */
  static DEFINE_HASHTABLE(unbound_pool_hash, UNBOUND_POOL_HASH_ORDER);
  
  /* I: attributes used when instantiating standard unbound pools on demand */
  static struct workqueue_attrs *unbound_std_wq_attrs[NR_STD_WORKER_POOLS];
  
  /* I: attributes used when instantiating ordered pools on demand */
  static struct workqueue_attrs *ordered_wq_attrs[NR_STD_WORKER_POOLS];
  
  struct workqueue_struct *system_wq __read_mostly;
  EXPORT_SYMBOL(system_wq);
  struct workqueue_struct *system_highpri_wq __read_mostly;
  EXPORT_SYMBOL_GPL(system_highpri_wq);
  struct workqueue_struct *system_long_wq __read_mostly;
  EXPORT_SYMBOL_GPL(system_long_wq);
  struct workqueue_struct *system_unbound_wq __read_mostly;
  EXPORT_SYMBOL_GPL(system_unbound_wq);
  struct workqueue_struct *system_freezable_wq __read_mostly;
  EXPORT_SYMBOL_GPL(system_freezable_wq);
  struct workqueue_struct *system_power_efficient_wq __read_mostly;
  EXPORT_SYMBOL_GPL(system_power_efficient_wq);
  struct workqueue_struct *system_freezable_power_efficient_wq __read_mostly;
  EXPORT_SYMBOL_GPL(system_freezable_power_efficient_wq);
  
  static int worker_thread(void *__worker);
  static void copy_workqueue_attrs(struct workqueue_attrs *to,
  				 const struct workqueue_attrs *from);
  
  #define CREATE_TRACE_POINTS
  #include <trace/events/workqueue.h>
  
  #define assert_rcu_or_pool_mutex()					\
  	rcu_lockdep_assert(rcu_read_lock_sched_held() ||		\
  			   lockdep_is_held(&wq_pool_mutex),		\
  			   "sched RCU or wq_pool_mutex should be held")
  
  #define assert_rcu_or_wq_mutex(wq)					\
  	rcu_lockdep_assert(rcu_read_lock_sched_held() ||		\
  			   lockdep_is_held(&wq->mutex),			\
  			   "sched RCU or wq->mutex should be held")
  
  #define for_each_cpu_worker_pool(pool, cpu)				\
  	for ((pool) = &per_cpu(cpu_worker_pools, cpu)[0];		\
  	     (pool) < &per_cpu(cpu_worker_pools, cpu)[NR_STD_WORKER_POOLS]; \
  	     (pool)++)
  
  /**
   * for_each_pool - iterate through all worker_pools in the system
   * @pool: iteration cursor
   * @pi: integer used for iteration
   *
   * This must be called either with wq_pool_mutex held or sched RCU read
   * locked.  If the pool needs to be used beyond the locking in effect, the
   * caller is responsible for guaranteeing that the pool stays online.
   *
   * The if/else clause exists only for the lockdep assertion and can be
   * ignored.
   */
  #define for_each_pool(pool, pi)						\
  	idr_for_each_entry(&worker_pool_idr, pool, pi)			\
  		if (({ assert_rcu_or_pool_mutex(); false; })) { }	\
  		else
  
  /**
   * for_each_pool_worker - iterate through all workers of a worker_pool
   * @worker: iteration cursor
   * @pool: worker_pool to iterate workers of
   *
   * This must be called with @pool->attach_mutex.
   *
   * The if/else clause exists only for the lockdep assertion and can be
   * ignored.
   */
  #define for_each_pool_worker(worker, pool)				\
  	list_for_each_entry((worker), &(pool)->workers, node)		\
  		if (({ lockdep_assert_held(&pool->attach_mutex); false; })) { } \
  		else
  
  /**
   * for_each_pwq - iterate through all pool_workqueues of the specified workqueue
   * @pwq: iteration cursor
   * @wq: the target workqueue
   *
   * This must be called either with wq->mutex held or sched RCU read locked.
   * If the pwq needs to be used beyond the locking in effect, the caller is
   * responsible for guaranteeing that the pwq stays online.
   *
   * The if/else clause exists only for the lockdep assertion and can be
   * ignored.
   */
  #define for_each_pwq(pwq, wq)						\
  	list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node)		\
  		if (({ assert_rcu_or_wq_mutex(wq); false; })) { }	\
  		else
  
  #ifdef CONFIG_DEBUG_OBJECTS_WORK
  
  static struct debug_obj_descr work_debug_descr;
  
  static void *work_debug_hint(void *addr)
  {
  	return ((struct work_struct *) addr)->func;
  }
  
  /*
   * fixup_init is called when:
   * - an active object is initialized
   */
  static int work_fixup_init(void *addr, enum debug_obj_state state)
  {
  	struct work_struct *work = addr;
  
  	switch (state) {
  	case ODEBUG_STATE_ACTIVE:
  		cancel_work_sync(work);
  		debug_object_init(work, &work_debug_descr);
  		return 1;
  	default:
  		return 0;
  	}
  }
  
  /*
   * fixup_activate is called when:
   * - an active object is activated
   * - an unknown object is activated (might be a statically initialized object)
   */
  static int work_fixup_activate(void *addr, enum debug_obj_state state)
  {
  	struct work_struct *work = addr;
  
  	switch (state) {
  
  	case ODEBUG_STATE_NOTAVAILABLE:
  		/*
  		 * This is not really a fixup. The work struct was
  		 * statically initialized. We just make sure that it
  		 * is tracked in the object tracker.
  		 */
  		if (test_bit(WORK_STRUCT_STATIC_BIT, work_data_bits(work))) {
  			debug_object_init(work, &work_debug_descr);
  			debug_object_activate(work, &work_debug_descr);
  			return 0;
  		}
  		WARN_ON_ONCE(1);
  		return 0;
  
  	case ODEBUG_STATE_ACTIVE:
  		WARN_ON(1);
  
  	default:
  		return 0;
  	}
  }
  
  /*
   * fixup_free is called when:
   * - an active object is freed
   */
  static int work_fixup_free(void *addr, enum debug_obj_state state)
  {
  	struct work_struct *work = addr;
  
  	switch (state) {
  	case ODEBUG_STATE_ACTIVE:
  		cancel_work_sync(work);
  		debug_object_free(work, &work_debug_descr);
  		return 1;
  	default:
  		return 0;
  	}
  }
  
  static struct debug_obj_descr work_debug_descr = {
  	.name		= "work_struct",
  	.debug_hint	= work_debug_hint,
  	.fixup_init	= work_fixup_init,
  	.fixup_activate	= work_fixup_activate,
  	.fixup_free	= work_fixup_free,
  };
  
  static inline void debug_work_activate(struct work_struct *work)
  {
  	debug_object_activate(work, &work_debug_descr);
  }
  
  static inline void debug_work_deactivate(struct work_struct *work)
  {
  	debug_object_deactivate(work, &work_debug_descr);
  }
  
  void __init_work(struct work_struct *work, int onstack)
  {
  	if (onstack)
  		debug_object_init_on_stack(work, &work_debug_descr);
  	else
  		debug_object_init(work, &work_debug_descr);
  }
  EXPORT_SYMBOL_GPL(__init_work);
  
  void destroy_work_on_stack(struct work_struct *work)
  {
  	debug_object_free(work, &work_debug_descr);
  }
  EXPORT_SYMBOL_GPL(destroy_work_on_stack);
  
  void destroy_delayed_work_on_stack(struct delayed_work *work)
  {
  	destroy_timer_on_stack(&work->timer);
  	debug_object_free(&work->work, &work_debug_descr);
  }
  EXPORT_SYMBOL_GPL(destroy_delayed_work_on_stack);
  
  #else
  static inline void debug_work_activate(struct work_struct *work) { }
  static inline void debug_work_deactivate(struct work_struct *work) { }
  #endif
  
  /**
   * worker_pool_assign_id - allocate ID and assing it to @pool
   * @pool: the pool pointer of interest
   *
   * Returns 0 if ID in [0, WORK_OFFQ_POOL_NONE) is allocated and assigned
   * successfully, -errno on failure.
   */
  static int worker_pool_assign_id(struct worker_pool *pool)
  {
  	int ret;
  
  	lockdep_assert_held(&wq_pool_mutex);
  
  	ret = idr_alloc(&worker_pool_idr, pool, 0, WORK_OFFQ_POOL_NONE,
  			GFP_KERNEL);
  	if (ret >= 0) {
  		pool->id = ret;
  		return 0;
  	}
  	return ret;
  }
  
  /**
   * unbound_pwq_by_node - return the unbound pool_workqueue for the given node
   * @wq: the target workqueue
   * @node: the node ID
   *
   * This must be called either with pwq_lock held or sched RCU read locked.
   * If the pwq needs to be used beyond the locking in effect, the caller is
   * responsible for guaranteeing that the pwq stays online.
   *
   * Return: The unbound pool_workqueue for @node.
   */
  static struct pool_workqueue *unbound_pwq_by_node(struct workqueue_struct *wq,
  						  int node)
  {
  	assert_rcu_or_wq_mutex(wq);
  	return rcu_dereference_raw(wq->numa_pwq_tbl[node]);
  }
  
  static unsigned int work_color_to_flags(int color)
  {
  	return color << WORK_STRUCT_COLOR_SHIFT;
  }
  
  static int get_work_color(struct work_struct *work)
  {
  	return (*work_data_bits(work) >> WORK_STRUCT_COLOR_SHIFT) &
  		((1 << WORK_STRUCT_COLOR_BITS) - 1);
  }
  
  static int work_next_color(int color)
  {
  	return (color + 1) % WORK_NR_COLORS;
  }
  
  /*
   * While queued, %WORK_STRUCT_PWQ is set and non flag bits of a work's data
   * contain the pointer to the queued pwq.  Once execution starts, the flag
   * is cleared and the high bits contain OFFQ flags and pool ID.
   *
   * set_work_pwq(), set_work_pool_and_clear_pending(), mark_work_canceling()
   * and clear_work_data() can be used to set the pwq, pool or clear
   * work->data.  These functions should only be called while the work is
   * owned - ie. while the PENDING bit is set.
   *
   * get_work_pool() and get_work_pwq() can be used to obtain the pool or pwq
   * corresponding to a work.  Pool is available once the work has been
   * queued anywhere after initialization until it is sync canceled.  pwq is
   * available only while the work item is queued.
   *
   * %WORK_OFFQ_CANCELING is used to mark a work item which is being
   * canceled.  While being canceled, a work item may have its PENDING set
   * but stay off timer and worklist for arbitrarily long and nobody should
   * try to steal the PENDING bit.
   */
  static inline void set_work_data(struct work_struct *work, unsigned long data,
  				 unsigned long flags)
  {
  	WARN_ON_ONCE(!work_pending(work));
  	atomic_long_set(&work->data, data | flags | work_static(work));
  }
  
  static void set_work_pwq(struct work_struct *work, struct pool_workqueue *pwq,
  			 unsigned long extra_flags)
  {
  	set_work_data(work, (unsigned long)pwq,
  		      WORK_STRUCT_PENDING | WORK_STRUCT_PWQ | extra_flags);
  }
  
  static void set_work_pool_and_keep_pending(struct work_struct *work,
  					   int pool_id)
  {
  	set_work_data(work, (unsigned long)pool_id << WORK_OFFQ_POOL_SHIFT,
  		      WORK_STRUCT_PENDING);
  }
  
  static void set_work_pool_and_clear_pending(struct work_struct *work,
  					    int pool_id)
  {
  	/*
  	 * The following wmb is paired with the implied mb in
  	 * test_and_set_bit(PENDING) and ensures all updates to @work made
  	 * here are visible to and precede any updates by the next PENDING
  	 * owner.
  	 */
  	smp_wmb();
  	set_work_data(work, (unsigned long)pool_id << WORK_OFFQ_POOL_SHIFT, 0);
  }
  
  static void clear_work_data(struct work_struct *work)
  {
  	smp_wmb();	/* see set_work_pool_and_clear_pending() */
  	set_work_data(work, WORK_STRUCT_NO_POOL, 0);
  }
  
  static struct pool_workqueue *get_work_pwq(struct work_struct *work)
  {
  	unsigned long data = atomic_long_read(&work->data);
  
  	if (data & WORK_STRUCT_PWQ)
  		return (void *)(data & WORK_STRUCT_WQ_DATA_MASK);
  	else
  		return NULL;
  }
  
  /**
   * get_work_pool - return the worker_pool a given work was associated with
   * @work: the work item of interest
   *
   * Pools are created and destroyed under wq_pool_mutex, and allows read
   * access under sched-RCU read lock.  As such, this function should be
   * called under wq_pool_mutex or with preemption disabled.
   *
   * All fields of the returned pool are accessible as long as the above
   * mentioned locking is in effect.  If the returned pool needs to be used
   * beyond the critical section, the caller is responsible for ensuring the
   * returned pool is and stays online.
   *
   * Return: The worker_pool @work was last associated with.  %NULL if none.
   */
  static struct worker_pool *get_work_pool(struct work_struct *work)
  {
  	unsigned long data = atomic_long_read(&work->data);
  	int pool_id;
  
  	assert_rcu_or_pool_mutex();
  
  	if (data & WORK_STRUCT_PWQ)
  		return ((struct pool_workqueue *)
  			(data & WORK_STRUCT_WQ_DATA_MASK))->pool;
  
  	pool_id = data >> WORK_OFFQ_POOL_SHIFT;
  	if (pool_id == WORK_OFFQ_POOL_NONE)
  		return NULL;
  
  	return idr_find(&worker_pool_idr, pool_id);
  }
  
  /**
   * get_work_pool_id - return the worker pool ID a given work is associated with
   * @work: the work item of interest
   *
   * Return: The worker_pool ID @work was last associated with.
   * %WORK_OFFQ_POOL_NONE if none.
   */
  static int get_work_pool_id(struct work_struct *work)
  {
  	unsigned long data = atomic_long_read(&work->data);
  
  	if (data & WORK_STRUCT_PWQ)
  		return ((struct pool_workqueue *)
  			(data & WORK_STRUCT_WQ_DATA_MASK))->pool->id;
  
  	return data >> WORK_OFFQ_POOL_SHIFT;
  }
  
  static void mark_work_canceling(struct work_struct *work)
  {
  	unsigned long pool_id = get_work_pool_id(work);
  
  	pool_id <<= WORK_OFFQ_POOL_SHIFT;
  	set_work_data(work, pool_id | WORK_OFFQ_CANCELING, WORK_STRUCT_PENDING);
  }
  
  static bool work_is_canceling(struct work_struct *work)
  {
  	unsigned long data = atomic_long_read(&work->data);
  
  	return !(data & WORK_STRUCT_PWQ) && (data & WORK_OFFQ_CANCELING);
  }
  
  /*
   * Policy functions.  These define the policies on how the global worker
   * pools are managed.  Unless noted otherwise, these functions assume that
   * they're being called with pool->lock held.
   */
  
  static bool __need_more_worker(struct worker_pool *pool)
  {
  	return !atomic_read(&pool->nr_running);
  }
  
  /*
   * Need to wake up a worker?  Called from anything but currently
   * running workers.
   *
   * Note that, because unbound workers never contribute to nr_running, this
   * function will always return %true for unbound pools as long as the
   * worklist isn't empty.
   */
  static bool need_more_worker(struct worker_pool *pool)
  {
  	return !list_empty(&pool->worklist) && __need_more_worker(pool);
  }
  
  /* Can I start working?  Called from busy but !running workers. */
  static bool may_start_working(struct worker_pool *pool)
  {
  	return pool->nr_idle;
  }
  
  /* Do I need to keep working?  Called from currently running workers. */
  static bool keep_working(struct worker_pool *pool)
  {
  	return !list_empty(&pool->worklist) &&
  		atomic_read(&pool->nr_running) <= 1;
  }
  
  /* Do we need a new worker?  Called from manager. */
  static bool need_to_create_worker(struct worker_pool *pool)
  {
  	return need_more_worker(pool) && !may_start_working(pool);
  }
  
  /* Do we have too many workers and should some go away? */
  static bool too_many_workers(struct worker_pool *pool)
  {
  	bool managing = mutex_is_locked(&pool->manager_arb);
  	int nr_idle = pool->nr_idle + managing; /* manager is considered idle */
  	int nr_busy = pool->nr_workers - nr_idle;
  
  	/*
  	 * nr_idle and idle_list may disagree if idle rebinding is in
  	 * progress.  Never return %true if idle_list is empty.
  	 */
  	if (list_empty(&pool->idle_list))
  		return false;
  
  	return nr_idle > 2 && (nr_idle - 2) * MAX_IDLE_WORKERS_RATIO >= nr_busy;
  }
  
  /*
   * Wake up functions.
   */
  
  /* Return the first idle worker.  Safe with preemption disabled */
  static struct worker *first_idle_worker(struct worker_pool *pool)
  {
  	if (unlikely(list_empty(&pool->idle_list)))
  		return NULL;
  
  	return list_first_entry(&pool->idle_list, struct worker, entry);
  }
  
  /**
   * wake_up_worker - wake up an idle worker
   * @pool: worker pool to wake worker from
   *
   * Wake up the first idle worker of @pool.
   *
   * CONTEXT:
   * spin_lock_irq(pool->lock).
   */
  static void wake_up_worker(struct worker_pool *pool)
  {
  	struct worker *worker = first_idle_worker(pool);
  
  	if (likely(worker))
  		wake_up_process(worker->task);
  }
  
  /**
   * wq_worker_waking_up - a worker is waking up
   * @task: task waking up
   * @cpu: CPU @task is waking up to
   *
   * This function is called during try_to_wake_up() when a worker is
   * being awoken.
   *
   * CONTEXT:
   * spin_lock_irq(rq->lock)
   */
  void wq_worker_waking_up(struct task_struct *task, int cpu)
  {
  	struct worker *worker = kthread_data(task);
  
  	if (!(worker->flags & WORKER_NOT_RUNNING)) {
  		WARN_ON_ONCE(worker->pool->cpu != cpu);
  		atomic_inc(&worker->pool->nr_running);
  	}
  }
  
  /**
   * wq_worker_sleeping - a worker is going to sleep
   * @task: task going to sleep
   * @cpu: CPU in question, must be the current CPU number
   *
   * This function is called during schedule() when a busy worker is
   * going to sleep.  Worker on the same cpu can be woken up by
   * returning pointer to its task.
   *
   * CONTEXT:
   * spin_lock_irq(rq->lock)
   *
   * Return:
   * Worker task on @cpu to wake up, %NULL if none.
   */
  struct task_struct *wq_worker_sleeping(struct task_struct *task, int cpu)
  {
  	struct worker *worker = kthread_data(task), *to_wakeup = NULL;
  	struct worker_pool *pool;
  
  	/*
  	 * Rescuers, which may not have all the fields set up like normal
  	 * workers, also reach here, let's not access anything before
  	 * checking NOT_RUNNING.
  	 */
  	if (worker->flags & WORKER_NOT_RUNNING)
  		return NULL;
  
  	pool = worker->pool;
  
  	/* this can only happen on the local cpu */
  	if (WARN_ON_ONCE(cpu != raw_smp_processor_id()))
  		return NULL;
  
  	/*
  	 * The counterpart of the following dec_and_test, implied mb,
  	 * worklist not empty test sequence is in insert_work().
  	 * Please read comment there.
  	 *
  	 * NOT_RUNNING is clear.  This means that we're bound to and
  	 * running on the local cpu w/ rq lock held and preemption
  	 * disabled, which in turn means that none else could be
  	 * manipulating idle_list, so dereferencing idle_list without pool
  	 * lock is safe.
  	 */
  	if (atomic_dec_and_test(&pool->nr_running) &&
  	    !list_empty(&pool->worklist))
  		to_wakeup = first_idle_worker(pool);
  	return to_wakeup ? to_wakeup->task : NULL;
  }
  
  /**
   * worker_set_flags - set worker flags and adjust nr_running accordingly
   * @worker: self
   * @flags: flags to set
   * @wakeup: wakeup an idle worker if necessary
   *
   * Set @flags in @worker->flags and adjust nr_running accordingly.  If
   * nr_running becomes zero and @wakeup is %true, an idle worker is
   * woken up.
   *
   * CONTEXT:
   * spin_lock_irq(pool->lock)
   */
  static inline void worker_set_flags(struct worker *worker, unsigned int flags,
  				    bool wakeup)
  {
  	struct worker_pool *pool = worker->pool;
  
  	WARN_ON_ONCE(worker->task != current);
  
  	/*
  	 * If transitioning into NOT_RUNNING, adjust nr_running and
  	 * wake up an idle worker as necessary if requested by
  	 * @wakeup.
  	 */
  	if ((flags & WORKER_NOT_RUNNING) &&
  	    !(worker->flags & WORKER_NOT_RUNNING)) {
  		if (wakeup) {
  			if (atomic_dec_and_test(&pool->nr_running) &&
  			    !list_empty(&pool->worklist))
  				wake_up_worker(pool);
  		} else
  			atomic_dec(&pool->nr_running);
  	}
  
  	worker->flags |= flags;
  }
  
  /**
   * worker_clr_flags - clear worker flags and adjust nr_running accordingly
   * @worker: self
   * @flags: flags to clear
   *
   * Clear @flags in @worker->flags and adjust nr_running accordingly.
   *
   * CONTEXT:
   * spin_lock_irq(pool->lock)
   */
  static inline void worker_clr_flags(struct worker *worker, unsigned int flags)
  {
  	struct worker_pool *pool = worker->pool;
  	unsigned int oflags = worker->flags;
  
  	WARN_ON_ONCE(worker->task != current);
  
  	worker->flags &= ~flags;
  
  	/*
  	 * If transitioning out of NOT_RUNNING, increment nr_running.  Note
  	 * that the nested NOT_RUNNING is not a noop.  NOT_RUNNING is mask
  	 * of multiple flags, not a single flag.
  	 */
  	if ((flags & WORKER_NOT_RUNNING) && (oflags & WORKER_NOT_RUNNING))
  		if (!(worker->flags & WORKER_NOT_RUNNING))
  			atomic_inc(&pool->nr_running);
  }
  
  /**
   * find_worker_executing_work - find worker which is executing a work
   * @pool: pool of interest
   * @work: work to find worker for
   *
   * Find a worker which is executing @work on @pool by searching
   * @pool->busy_hash which is keyed by the address of @work.  For a worker
   * to match, its current execution should match the address of @work and
   * its work function.  This is to avoid unwanted dependency between
   * unrelated work executions through a work item being recycled while still
   * being executed.
   *
   * This is a bit tricky.  A work item may be freed once its execution
   * starts and nothing prevents the freed area from being recycled for
   * another work item.  If the same work item address ends up being reused
   * before the original execution finishes, workqueue will identify the
   * recycled work item as currently executing and make it wait until the
   * current execution finishes, introducing an unwanted dependency.
   *
   * This function checks the work item address and work function to avoid
   * false positives.  Note that this isn't complete as one may construct a
   * work function which can introduce dependency onto itself through a
   * recycled work item.  Well, if somebody wants to shoot oneself in the
   * foot that badly, there's only so much we can do, and if such deadlock
   * actually occurs, it should be easy to locate the culprit work function.
   *
   * CONTEXT:
   * spin_lock_irq(pool->lock).
   *
   * Return:
   * Pointer to worker which is executing @work if found, %NULL
   * otherwise.
   */
  static struct worker *find_worker_executing_work(struct worker_pool *pool,
  						 struct work_struct *work)
  {
  	struct worker *worker;
  
  	hash_for_each_possible(pool->busy_hash, worker, hentry,
  			       (unsigned long)work)
  		if (worker->current_work == work &&
  		    worker->current_func == work->func)
  			return worker;
  
  	return NULL;
  }
  
  /**
   * move_linked_works - move linked works to a list
   * @work: start of series of works to be scheduled
   * @head: target list to append @work to
   * @nextp: out paramter for nested worklist walking
   *
   * Schedule linked works starting from @work to @head.  Work series to
   * be scheduled starts at @work and includes any consecutive work with
   * WORK_STRUCT_LINKED set in its predecessor.
   *
   * If @nextp is not NULL, it's updated to point to the next work of
   * the last scheduled work.  This allows move_linked_works() to be
   * nested inside outer list_for_each_entry_safe().
   *
   * CONTEXT:
   * spin_lock_irq(pool->lock).
   */
  static void move_linked_works(struct work_struct *work, struct list_head *head,
  			      struct work_struct **nextp)
  {
  	struct work_struct *n;
  
  	/*
  	 * Linked worklist will always end before the end of the list,
  	 * use NULL for list head.
  	 */
  	list_for_each_entry_safe_from(work, n, NULL, entry) {
  		list_move_tail(&work->entry, head);
  		if (!(*work_data_bits(work) & WORK_STRUCT_LINKED))
  			break;
  	}
  
  	/*
  	 * If we're already inside safe list traversal and have moved
  	 * multiple works to the scheduled queue, the next position
  	 * needs to be updated.
  	 */
  	if (nextp)
  		*nextp = n;
  }
  
  /**
   * get_pwq - get an extra reference on the specified pool_workqueue
   * @pwq: pool_workqueue to get
   *
   * Obtain an extra reference on @pwq.  The caller should guarantee that
   * @pwq has positive refcnt and be holding the matching pool->lock.
   */
  static void get_pwq(struct pool_workqueue *pwq)
  {
  	lockdep_assert_held(&pwq->pool->lock);
  	WARN_ON_ONCE(pwq->refcnt <= 0);
  	pwq->refcnt++;
  }
  
  /**
   * put_pwq - put a pool_workqueue reference
   * @pwq: pool_workqueue to put
   *
   * Drop a reference of @pwq.  If its refcnt reaches zero, schedule its
   * destruction.  The caller should be holding the matching pool->lock.
   */
  static void put_pwq(struct pool_workqueue *pwq)
  {
  	lockdep_assert_held(&pwq->pool->lock);
  	if (likely(--pwq->refcnt))
  		return;
  	if (WARN_ON_ONCE(!(pwq->wq->flags & WQ_UNBOUND)))
  		return;
  	/*
  	 * @pwq can't be released under pool->lock, bounce to
  	 * pwq_unbound_release_workfn().  This never recurses on the same
  	 * pool->lock as this path is taken only for unbound workqueues and
  	 * the release work item is scheduled on a per-cpu workqueue.  To
  	 * avoid lockdep warning, unbound pool->locks are given lockdep
  	 * subclass of 1 in get_unbound_pool().
  	 */
  	schedule_work(&pwq->unbound_release_work);
  }
  
  /**
   * put_pwq_unlocked - put_pwq() with surrounding pool lock/unlock
   * @pwq: pool_workqueue to put (can be %NULL)
   *
   * put_pwq() with locking.  This function also allows %NULL @pwq.
   */
  static void put_pwq_unlocked(struct pool_workqueue *pwq)
  {
  	if (pwq) {
  		/*
  		 * As both pwqs and pools are sched-RCU protected, the
  		 * following lock operations are safe.
  		 */
  		spin_lock_irq(&pwq->pool->lock);
  		put_pwq(pwq);
  		spin_unlock_irq(&pwq->pool->lock);
  	}
  }
  
  static void pwq_activate_delayed_work(struct work_struct *work)
  {
  	struct pool_workqueue *pwq = get_work_pwq(work);
  
  	trace_workqueue_activate_work(work);
  	move_linked_works(work, &pwq->pool->worklist, NULL);
  	__clear_bit(WORK_STRUCT_DELAYED_BIT, work_data_bits(work));
  	pwq->nr_active++;
  }
  
  static void pwq_activate_first_delayed(struct pool_workqueue *pwq)
  {
  	struct work_struct *work = list_first_entry(&pwq->delayed_works,
  						    struct work_struct, entry);
  
  	pwq_activate_delayed_work(work);
  }
  
  /**
   * pwq_dec_nr_in_flight - decrement pwq's nr_in_flight
   * @pwq: pwq of interest
   * @color: color of work which left the queue
   *
   * A work either has completed or is removed from pending queue,
   * decrement nr_in_flight of its pwq and handle workqueue flushing.
   *
   * CONTEXT:
   * spin_lock_irq(pool->lock).
   */
  static void pwq_dec_nr_in_flight(struct pool_workqueue *pwq, int color)
  {
  	/* uncolored work items don't participate in flushing or nr_active */
  	if (color == WORK_NO_COLOR)
  		goto out_put;
  
  	pwq->nr_in_flight[color]--;
  
  	pwq->nr_active--;
  	if (!list_empty(&pwq->delayed_works)) {
  		/* one down, submit a delayed one */
  		if (pwq->nr_active < pwq->max_active)
  			pwq_activate_first_delayed(pwq);
  	}
  
  	/* is flush in progress and are we at the flushing tip? */
  	if (likely(pwq->flush_color != color))
  		goto out_put;
  
  	/* are there still in-flight works? */
  	if (pwq->nr_in_flight[color])
  		goto out_put;
  
  	/* this pwq is done, clear flush_color */
  	pwq->flush_color = -1;
  
  	/*
  	 * If this was the last pwq, wake up the first flusher.  It
  	 * will handle the rest.
  	 */
  	if (atomic_dec_and_test(&pwq->wq->nr_pwqs_to_flush))
  		complete(&pwq->wq->first_flusher->done);
  out_put:
  	put_pwq(pwq);
  }
  
  /**
   * try_to_grab_pending - steal work item from worklist and disable irq
   * @work: work item to steal
   * @is_dwork: @work is a delayed_work
   * @flags: place to store irq state
   *
   * Try to grab PENDING bit of @work.  This function can handle @work in any
   * stable state - idle, on timer or on worklist.
   *
   * Return:
   *  1		if @work was pending and we successfully stole PENDING
   *  0		if @work was idle and we claimed PENDING
   *  -EAGAIN	if PENDING couldn't be grabbed at the moment, safe to busy-retry
   *  -ENOENT	if someone else is canceling @work, this state may persist
   *		for arbitrarily long
   *
   * Note:
   * On >= 0 return, the caller owns @work's PENDING bit.  To avoid getting
   * interrupted while holding PENDING and @work off queue, irq must be
   * disabled on entry.  This, combined with delayed_work->timer being
   * irqsafe, ensures that we return -EAGAIN for finite short period of time.
   *
   * On successful return, >= 0, irq is disabled and the caller is
   * responsible for releasing it using local_irq_restore(*@flags).
   *
   * This function is safe to call from any context including IRQ handler.
   */
  static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
  			       unsigned long *flags)
  {
  	struct worker_pool *pool;
  	struct pool_workqueue *pwq;
  
  	local_irq_save(*flags);
  
  	/* try to steal the timer if it exists */
  	if (is_dwork) {
  		struct delayed_work *dwork = to_delayed_work(work);
  
  		/*
  		 * dwork->timer is irqsafe.  If del_timer() fails, it's
  		 * guaranteed that the timer is not queued anywhere and not
  		 * running on the local CPU.
  		 */
  		if (likely(del_timer(&dwork->timer)))
  			return 1;
  	}
  
  	/* try to claim PENDING the normal way */
  	if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)))
  		return 0;
  
  	/*
  	 * The queueing is in progress, or it is already queued. Try to
  	 * steal it from ->worklist without clearing WORK_STRUCT_PENDING.
  	 */
  	pool = get_work_pool(work);
  	if (!pool)
  		goto fail;
  
  	spin_lock(&pool->lock);
  	/*
  	 * work->data is guaranteed to point to pwq only while the work
  	 * item is queued on pwq->wq, and both updating work->data to point
  	 * to pwq on queueing and to pool on dequeueing are done under
  	 * pwq->pool->lock.  This in turn guarantees that, if work->data
  	 * points to pwq which is associated with a locked pool, the work
  	 * item is currently queued on that pool.
  	 */
  	pwq = get_work_pwq(work);
  	if (pwq && pwq->pool == pool) {
  		debug_work_deactivate(work);
  
  		/*
  		 * A delayed work item cannot be grabbed directly because
  		 * it might have linked NO_COLOR work items which, if left
  		 * on the delayed_list, will confuse pwq->nr_active
  		 * management later on and cause stall.  Make sure the work
  		 * item is activated before grabbing.
  		 */
  		if (*work_data_bits(work) & WORK_STRUCT_DELAYED)
  			pwq_activate_delayed_work(work);
  
  		list_del_init(&work->entry);
  		pwq_dec_nr_in_flight(get_work_pwq(work), get_work_color(work));
  
  		/* work->data points to pwq iff queued, point to pool */
  		set_work_pool_and_keep_pending(work, pool->id);
  
  		spin_unlock(&pool->lock);
  		return 1;
  	}
  	spin_unlock(&pool->lock);
  fail:
  	local_irq_restore(*flags);
  	if (work_is_canceling(work))
  		return -ENOENT;
  	cpu_relax();
  	return -EAGAIN;
  }
  
  /**
   * insert_work - insert a work into a pool
   * @pwq: pwq @work belongs to
   * @work: work to insert
   * @head: insertion point
   * @extra_flags: extra WORK_STRUCT_* flags to set
   *
   * Insert @work which belongs to @pwq after @head.  @extra_flags is or'd to
   * work_struct flags.
   *
   * CONTEXT:
   * spin_lock_irq(pool->lock).
   */
  static void insert_work(struct pool_workqueue *pwq, struct work_struct *work,
  			struct list_head *head, unsigned int extra_flags)
  {
  	struct worker_pool *pool = pwq->pool;
  
  	/* we own @work, set data and link */
  	set_work_pwq(work, pwq, extra_flags);
  	list_add_tail(&work->entry, head);
  	get_pwq(pwq);
  
  	/*
  	 * Ensure either wq_worker_sleeping() sees the above
  	 * list_add_tail() or we see zero nr_running to avoid workers lying
  	 * around lazily while there are works to be processed.
  	 */
  	smp_mb();
  
  	if (__need_more_worker(pool))
  		wake_up_worker(pool);
  }
  
  /*
   * Test whether @work is being queued from another work executing on the
   * same workqueue.
   */
  static bool is_chained_work(struct workqueue_struct *wq)
  {
  	struct worker *worker;
  
  	worker = current_wq_worker();
  	/*
  	 * Return %true iff I'm a worker execuing a work item on @wq.  If
  	 * I'm @worker, it's safe to dereference it without locking.
  	 */
  	return worker && worker->current_pwq->wq == wq;
  }
  
  static void __queue_work(int cpu, struct workqueue_struct *wq,
  			 struct work_struct *work)
  {
  	struct pool_workqueue *pwq;
  	struct worker_pool *last_pool;
  	struct list_head *worklist;
  	unsigned int work_flags;
  	unsigned int req_cpu = cpu;
  
  	/*
  	 * While a work item is PENDING && off queue, a task trying to
  	 * steal the PENDING will busy-loop waiting for it to either get
  	 * queued or lose PENDING.  Grabbing PENDING and queueing should
  	 * happen with IRQ disabled.
  	 */
  	WARN_ON_ONCE(!irqs_disabled());
  
  	debug_work_activate(work);
  
  	/* if draining, only works from the same workqueue are allowed */
  	if (unlikely(wq->flags & __WQ_DRAINING) &&
  	    WARN_ON_ONCE(!is_chained_work(wq)))
  		return;
  retry:
  	if (req_cpu == WORK_CPU_UNBOUND)
  		cpu = raw_smp_processor_id();
  
  	/* pwq which will be used unless @work is executing elsewhere */
  	if (!(wq->flags & WQ_UNBOUND))
  		pwq = per_cpu_ptr(wq->cpu_pwqs, cpu);
  	else
  		pwq = unbound_pwq_by_node(wq, cpu_to_node(cpu));
  
  	/*
  	 * If @work was previously on a different pool, it might still be
  	 * running there, in which case the work needs to be queued on that
  	 * pool to guarantee non-reentrancy.
  	 */
  	last_pool = get_work_pool(work);
  	if (last_pool && last_pool != pwq->pool) {
  		struct worker *worker;
  
  		spin_lock(&last_pool->lock);
  
  		worker = find_worker_executing_work(last_pool, work);
  
  		if (worker && worker->current_pwq->wq == wq) {
  			pwq = worker->current_pwq;
  		} else {
  			/* meh... not running there, queue here */
  			spin_unlock(&last_pool->lock);
  			spin_lock(&pwq->pool->lock);
  		}
  	} else {
  		spin_lock(&pwq->pool->lock);
  	}
  
  	/*
  	 * pwq is determined and locked.  For unbound pools, we could have
  	 * raced with pwq release and it could already be dead.  If its
  	 * refcnt is zero, repeat pwq selection.  Note that pwqs never die
  	 * without another pwq replacing it in the numa_pwq_tbl or while
  	 * work items are executing on it, so the retrying is guaranteed to
  	 * make forward-progress.
  	 */
  	if (unlikely(!pwq->refcnt)) {
  		if (wq->flags & WQ_UNBOUND) {
  			spin_unlock(&pwq->pool->lock);
  			cpu_relax();
  			goto retry;
  		}
  		/* oops */
  		WARN_ONCE(true, "workqueue: per-cpu pwq for %s on cpu%d has 0 refcnt",
  			  wq->name, cpu);
  	}
  
  	/* pwq determined, queue */
  	trace_workqueue_queue_work(req_cpu, pwq, work);
  
  	if (WARN_ON(!list_empty(&work->entry))) {
  		spin_unlock(&pwq->pool->lock);
  		return;
  	}
  
  	pwq->nr_in_flight[pwq->work_color]++;
  	work_flags = work_color_to_flags(pwq->work_color);
  
  	if (likely(pwq->nr_active < pwq->max_active)) {
  		trace_workqueue_activate_work(work);
  		pwq->nr_active++;
  		worklist = &pwq->pool->worklist;
  	} else {
  		work_flags |= WORK_STRUCT_DELAYED;
  		worklist = &pwq->delayed_works;
  	}
  
  	insert_work(pwq, work, worklist, work_flags);
  
  	spin_unlock(&pwq->pool->lock);
  }
  
  /**
   * queue_work_on - queue work on specific cpu
   * @cpu: CPU number to execute work on
   * @wq: workqueue to use
   * @work: work to queue
   *
   * We queue the work to a specific CPU, the caller must ensure it
   * can't go away.
   *
   * Return: %false if @work was already on a queue, %true otherwise.
   */
  bool queue_work_on(int cpu, struct workqueue_struct *wq,
  		   struct work_struct *work)
  {
  	bool ret = false;
  	unsigned long flags;
  
  	local_irq_save(flags);
  
  	if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
  		__queue_work(cpu, wq, work);
  		ret = true;
  	}
  
  	local_irq_restore(flags);
  	return ret;
  }
  EXPORT_SYMBOL(queue_work_on);
  
  void delayed_work_timer_fn(unsigned long __data)
  {
  	struct delayed_work *dwork = (struct delayed_work *)__data;
  
  	/* should have been called from irqsafe timer with irq already off */
  	__queue_work(dwork->cpu, dwork->wq, &dwork->work);
  }
  EXPORT_SYMBOL(delayed_work_timer_fn);
  
  static void __queue_delayed_work(int cpu, struct workqueue_struct *wq,
  				struct delayed_work *dwork, unsigned long delay)
  {
  	struct timer_list *timer = &dwork->timer;
  	struct work_struct *work = &dwork->work;
  
  	WARN_ON_ONCE(timer->function != delayed_work_timer_fn ||
  		     timer->data != (unsigned long)dwork);
  	WARN_ON_ONCE(timer_pending(timer));
  	WARN_ON_ONCE(!list_empty(&work->entry));
  
  	/*
  	 * If @delay is 0, queue @dwork->work immediately.  This is for
  	 * both optimization and correctness.  The earliest @timer can
  	 * expire is on the closest next tick and delayed_work users depend
  	 * on that there's no such delay when @delay is 0.
  	 */
  	if (!delay) {
  		__queue_work(cpu, wq, &dwork->work);
  		return;
  	}
  
  	timer_stats_timer_set_start_info(&dwork->timer);
  
  	dwork->wq = wq;
  	dwork->cpu = cpu;
  	timer->expires = jiffies + delay;
  
  	if (unlikely(cpu != WORK_CPU_UNBOUND))
  		add_timer_on(timer, cpu);
  	else
  		add_timer(timer);
  }
  
  /**
   * queue_delayed_work_on - queue work on specific CPU after delay
   * @cpu: CPU number to execute work on
   * @wq: workqueue to use
   * @dwork: work to queue
   * @delay: number of jiffies to wait before queueing
   *
   * Return: %false if @work was already on a queue, %true otherwise.  If
   * @delay is zero and @dwork is idle, it will be scheduled for immediate
   * execution.
   */
  bool queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
  			   struct delayed_work *dwork, unsigned long delay)
  {
  	struct work_struct *work = &dwork->work;
  	bool ret = false;
  	unsigned long flags;
  
  	/* read the comment in __queue_work() */
  	local_irq_save(flags);
  
  	if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
  		__queue_delayed_work(cpu, wq, dwork, delay);
  		ret = true;
  	}
  
  	local_irq_restore(flags);
  	return ret;
  }
  EXPORT_SYMBOL(queue_delayed_work_on);
  
  /**
   * mod_delayed_work_on - modify delay of or queue a delayed work on specific CPU
   * @cpu: CPU number to execute work on
   * @wq: workqueue to use
   * @dwork: work to queue
   * @delay: number of jiffies to wait before queueing
   *
   * If @dwork is idle, equivalent to queue_delayed_work_on(); otherwise,
   * modify @dwork's timer so that it expires after @delay.  If @delay is
   * zero, @work is guaranteed to be scheduled immediately regardless of its
   * current state.
   *
   * Return: %false if @dwork was idle and queued, %true if @dwork was
   * pending and its timer was modified.
   *
   * This function is safe to call from any context including IRQ handler.
   * See try_to_grab_pending() for details.
   */
  bool mod_delayed_work_on(int cpu, struct workqueue_struct *wq,
  			 struct delayed_work *dwork, unsigned long delay)
  {
  	unsigned long flags;
  	int ret;
  
  	do {
  		ret = try_to_grab_pending(&dwork->work, true, &flags);
  	} while (unlikely(ret == -EAGAIN));
  
  	if (likely(ret >= 0)) {
  		__queue_delayed_work(cpu, wq, dwork, delay);
  		local_irq_restore(flags);
  	}
  
  	/* -ENOENT from try_to_grab_pending() becomes %true */
  	return ret;
  }
  EXPORT_SYMBOL_GPL(mod_delayed_work_on);
  
  /**
   * worker_enter_idle - enter idle state
   * @worker: worker which is entering idle state
   *
   * @worker is entering idle state.  Update stats and idle timer if
   * necessary.
   *
   * LOCKING:
   * spin_lock_irq(pool->lock).
   */
  static void worker_enter_idle(struct worker *worker)
  {
  	struct worker_pool *pool = worker->pool;
  
  	if (WARN_ON_ONCE(worker->flags & WORKER_IDLE) ||
  	    WARN_ON_ONCE(!list_empty(&worker->entry) &&
  			 (worker->hentry.next || worker->hentry.pprev)))
  		return;
  
  	/* can't use worker_set_flags(), also called from start_worker() */
  	worker->flags |= WORKER_IDLE;
  	pool->nr_idle++;
  	worker->last_active = jiffies;
  
  	/* idle_list is LIFO */
  	list_add(&worker->entry, &pool->idle_list);
  
  	if (too_many_workers(pool) && !timer_pending(&pool->idle_timer))
  		mod_timer(&pool->idle_timer, jiffies + IDLE_WORKER_TIMEOUT);
  
  	/*
  	 * Sanity check nr_running.  Because wq_unbind_fn() releases
  	 * pool->lock between setting %WORKER_UNBOUND and zapping
  	 * nr_running, the warning may trigger spuriously.  Check iff
  	 * unbind is not in progress.
  	 */
  	WARN_ON_ONCE(!(pool->flags & POOL_DISASSOCIATED) &&
  		     pool->nr_workers == pool->nr_idle &&
  		     atomic_read(&pool->nr_running));
  }
  
  /**
   * worker_leave_idle - leave idle state
   * @worker: worker which is leaving idle state
   *
   * @worker is leaving idle state.  Update stats.
   *
   * LOCKING:
   * spin_lock_irq(pool->lock).
   */
  static void worker_leave_idle(struct worker *worker)
  {
  	struct worker_pool *pool = worker->pool;
  
  	if (WARN_ON_ONCE(!(worker->flags & WORKER_IDLE)))
  		return;
  	worker_clr_flags(worker, WORKER_IDLE);
  	pool->nr_idle--;
  	list_del_init(&worker->entry);
  }
  
  static struct worker *alloc_worker(void)
  {
  	struct worker *worker;
  
  	worker = kzalloc(sizeof(*worker), GFP_KERNEL);
  	if (worker) {
  		INIT_LIST_HEAD(&worker->entry);
  		INIT_LIST_HEAD(&worker->scheduled);
  		INIT_LIST_HEAD(&worker->node);
  		/* on creation a worker is in !idle && prep state */
  		worker->flags = WORKER_PREP;
  	}
  	return worker;
  }
  
  /**
   * worker_attach_to_pool() - attach a worker to a pool
   * @worker: worker to be attached
   * @pool: the target pool
   *
   * Attach @worker to @pool.  Once attached, the %WORKER_UNBOUND flag and
   * cpu-binding of @worker are kept coordinated with the pool across
   * cpu-[un]hotplugs.
   */
  static void worker_attach_to_pool(struct worker *worker,
  				   struct worker_pool *pool)
  {
  	mutex_lock(&pool->attach_mutex);
  
  	/*
  	 * set_cpus_allowed_ptr() will fail if the cpumask doesn't have any
  	 * online CPUs.  It'll be re-applied when any of the CPUs come up.
  	 */
  	set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);
  
  	/*
  	 * The pool->attach_mutex ensures %POOL_DISASSOCIATED remains
  	 * stable across this function.  See the comments above the
  	 * flag definition for details.
  	 */
  	if (pool->flags & POOL_DISASSOCIATED)
  		worker->flags |= WORKER_UNBOUND;
  
  	list_add_tail(&worker->node, &pool->workers);
  
  	mutex_unlock(&pool->attach_mutex);
  }
  
  /**
   * worker_detach_from_pool() - detach a worker from its pool
   * @worker: worker which is attached to its pool
   * @pool: the pool @worker is attached to
   *
   * Undo the attaching which had been done in worker_attach_to_pool().  The
   * caller worker shouldn't access to the pool after detached except it has
   * other reference to the pool.
   */
  static void worker_detach_from_pool(struct worker *worker,
  				    struct worker_pool *pool)
  {
  	struct completion *detach_completion = NULL;
  
  	mutex_lock(&pool->attach_mutex);
  	list_del(&worker->node);
  	if (list_empty(&pool->workers))
  		detach_completion = pool->detach_completion;
  	mutex_unlock(&pool->attach_mutex);
  
  	if (detach_completion)
  		complete(detach_completion);
  }
  
  /**
   * create_worker - create a new workqueue worker
   * @pool: pool the new worker will belong to
   *
   * Create a new worker which is attached to @pool.  The new worker must be
   * started by start_worker().
   *
   * CONTEXT:
   * Might sleep.  Does GFP_KERNEL allocations.
   *
   * Return:
   * Pointer to the newly created worker.
   */
  static struct worker *create_worker(struct worker_pool *pool)
  {
  	struct worker *worker = NULL;
  	int id = -1;
  	char id_buf[16];
  
  	/* ID is needed to determine kthread name */
  	id = ida_simple_get(&pool->worker_ida, 0, 0, GFP_KERNEL);
  	if (id < 0)
  		goto fail;
  
  	worker = alloc_worker();
  	if (!worker)
  		goto fail;
  
  	worker->pool = pool;
  	worker->id = id;
  
  	if (pool->cpu >= 0)
  		snprintf(id_buf, sizeof(id_buf), "%d:%d%s", pool->cpu, id,
  			 pool->attrs->nice < 0  ? "H" : "");
  	else
  		snprintf(id_buf, sizeof(id_buf), "u%d:%d", pool->id, id);
  
  	worker->task = kthread_create_on_node(worker_thread, worker, pool->node,
  					      "kworker/%s", id_buf);
  	if (IS_ERR(worker->task))
  		goto fail;
  
  	set_user_nice(worker->task, pool->attrs->nice);
  
  	/* prevent userland from meddling with cpumask of workqueue workers */
  	worker->task->flags |= PF_NO_SETAFFINITY;
  
  	/* successful, attach the worker to the pool */
  	worker_attach_to_pool(worker, pool);
  
  	return worker;
  
  fail:
  	if (id >= 0)
  		ida_simple_remove(&pool->worker_ida, id);
  	kfree(worker);
  	return NULL;
  }
  
  /**
   * start_worker - start a newly created worker
   * @worker: worker to start
   *
   * Make the pool aware of @worker and start it.
   *
   * CONTEXT:
   * spin_lock_irq(pool->lock).
   */
  static void start_worker(struct worker *worker)
  {
  	worker->pool->nr_workers++;
  	worker_enter_idle(worker);
  	wake_up_process(worker->task);
  }
  
  /**
   * create_and_start_worker - create and start a worker for a pool
   * @pool: the target pool
   *
   * Grab the managership of @pool and create and start a new worker for it.
   *
   * Return: 0 on success. A negative error code otherwise.
   */
  static int create_and_start_worker(struct worker_pool *pool)
  {
  	struct worker *worker;
  
  	worker = create_worker(pool);
  	if (worker) {
  		spin_lock_irq(&pool->lock);
  		start_worker(worker);
  		spin_unlock_irq(&pool->lock);
  	}
  
  	return worker ? 0 : -ENOMEM;
  }
  
  /**
   * destroy_worker - destroy a workqueue worker
   * @worker: worker to be destroyed
   *
   * Destroy @worker and adjust @pool stats accordingly.  The worker should
   * be idle.
   *
   * CONTEXT:
   * spin_lock_irq(pool->lock).
   */
  static void destroy_worker(struct worker *worker)
  {
  	struct worker_pool *pool = worker->pool;
  
  	lockdep_assert_held(&pool->lock);
  
  	/* sanity check frenzy */
  	if (WARN_ON(worker->current_work) ||
  	    WARN_ON(!list_empty(&worker->scheduled)) ||
  	    WARN_ON(!(worker->flags & WORKER_IDLE)))
  		return;
  
  	pool->nr_workers--;
  	pool->nr_idle--;
  
  	list_del_init(&worker->entry);
  	worker->flags |= WORKER_DIE;
  	wake_up_process(worker->task);
  }
  
  static void idle_worker_timeout(unsigned long __pool)
  {
  	struct worker_pool *pool = (void *)__pool;
  
  	spin_lock_irq(&pool->lock);
  
  	while (too_many_workers(pool)) {
  		struct worker *worker;
  		unsigned long expires;
  
  		/* idle_list is kept in LIFO order, check the last one */
  		worker = list_entry(pool->idle_list.prev, struct worker, entry);
  		expires = worker->last_active + IDLE_WORKER_TIMEOUT;
  
  		if (time_before(jiffies, expires)) {
  			mod_timer(&pool->idle_timer, expires);
  			break;
  		}
  
  		destroy_worker(worker);
  	}
  
  	spin_unlock_irq(&pool->lock);
  }
  
  static void send_mayday(struct work_struct *work)
  {
  	struct pool_workqueue *pwq = get_work_pwq(work);
  	struct workqueue_struct *wq = pwq->wq;
  
  	lockdep_assert_held(&wq_mayday_lock);
  
  	if (!wq->rescuer)
  		return;
  
  	/* mayday mayday mayday */
  	if (list_empty(&pwq->mayday_node)) {
  		/*
  		 * If @pwq is for an unbound wq, its base ref may be put at
  		 * any time due to an attribute change.  Pin @pwq until the
  		 * rescuer is done with it.
  		 */
  		get_pwq(pwq);
  		list_add_tail(&pwq->mayday_node, &wq->maydays);
  		wake_up_process(wq->rescuer->task);
  	}
  }
  
  static void pool_mayday_timeout(unsigned long __pool)
  {
  	struct worker_pool *pool = (void *)__pool;
  	struct work_struct *work;
  
  	spin_lock_irq(&wq_mayday_lock);		/* for wq->maydays */
  	spin_lock(&pool->lock);
  
  	if (need_to_create_worker(pool)) {
  		/*
  		 * We've been trying to create a new worker but
  		 * haven't been successful.  We might be hitting an
  		 * allocation deadlock.  Send distress signals to
  		 * rescuers.
  		 */
  		list_for_each_entry(work, &pool->worklist, entry)
  			send_mayday(work);
  	}
  
  	spin_unlock(&pool->lock);
  	spin_unlock_irq(&wq_mayday_lock);
  
  	mod_timer(&pool->mayday_timer, jiffies + MAYDAY_INTERVAL);
  }
  
  /**
   * maybe_create_worker - create a new worker if necessary
   * @pool: pool to create a new worker for
   *
   * Create a new worker for @pool if necessary.  @pool is guaranteed to
   * have at least one idle worker on return from this function.  If
   * creating a new worker takes longer than MAYDAY_INTERVAL, mayday is
   * sent to all rescuers with works scheduled on @pool to resolve
   * possible allocation deadlock.
   *
   * On return, need_to_create_worker() is guaranteed to be %false and
   * may_start_working() %true.
   *
   * LOCKING:
   * spin_lock_irq(pool->lock) which may be released and regrabbed
   * multiple times.  Does GFP_KERNEL allocations.  Called only from
   * manager.
   *
   * Return:
   * %false if no action was taken and pool->lock stayed locked, %true
   * otherwise.
   */
  static bool maybe_create_worker(struct worker_pool *pool)
  __releases(&pool->lock)
  __acquires(&pool->lock)
  {
  	if (!need_to_create_worker(pool))
  		return false;
  restart:
  	spin_unlock_irq(&pool->lock);
  
  	/* if we don't make progress in MAYDAY_INITIAL_TIMEOUT, call for help */
  	mod_timer(&pool->mayday_timer, jiffies + MAYDAY_INITIAL_TIMEOUT);
  
  	while (true) {
  		struct worker *worker;
  
  		worker = create_worker(pool);
  		if (worker) {
  			del_timer_sync(&pool->mayday_timer);
  			spin_lock_irq(&pool->lock);
  			start_worker(worker);
  			if (WARN_ON_ONCE(need_to_create_worker(pool)))
  				goto restart;
  			return true;
  		}
  
  		if (!need_to_create_worker(pool))
  			break;
  
  		__set_current_state(TASK_INTERRUPTIBLE);
  		schedule_timeout(CREATE_COOLDOWN);
  
  		if (!need_to_create_worker(pool))
  			break;
  	}
  
  	del_timer_sync(&pool->mayday_timer);
  	spin_lock_irq(&pool->lock);
  	if (need_to_create_worker(pool))
  		goto restart;
  	return true;
  }
  
  /**
   * manage_workers - manage worker pool
   * @worker: self
   *
   * Assume the manager role and manage the worker pool @worker belongs
   * to.  At any given time, there can be only zero or one manager per
   * pool.  The exclusion is handled automatically by this function.
   *
   * The caller can safely start processing works on false return.  On
   * true return, it's guaranteed that need_to_create_worker() is false
   * and may_start_working() is true.
   *
   * CONTEXT:
   * spin_lock_irq(pool->lock) which may be released and regrabbed
   * multiple times.  Does GFP_KERNEL allocations.
   *
   * Return:
   * %false if the pool don't need management and the caller can safely start
   * processing works, %true indicates that the function released pool->lock
   * and reacquired it to perform some management function and that the
   * conditions that the caller verified while holding the lock before
   * calling the function might no longer be true.
   */
  static bool manage_workers(struct worker *worker)
  {
  	struct worker_pool *pool = worker->pool;
  	bool ret = false;
  
  	/*
  	 * Anyone who successfully grabs manager_arb wins the arbitration
  	 * and becomes the manager.  mutex_trylock() on pool->manager_arb
  	 * failure while holding pool->lock reliably indicates that someone
  	 * else is managing the pool and the worker which failed trylock
  	 * can proceed to executing work items.  This means that anyone
  	 * grabbing manager_arb is responsible for actually performing
  	 * manager duties.  If manager_arb is grabbed and released without
  	 * actual management, the pool may stall indefinitely.
  	 */
  	if (!mutex_trylock(&pool->manager_arb))
  		return ret;
  
  	ret |= maybe_create_worker(pool);
  
  	mutex_unlock(&pool->manager_arb);
  	return ret;
  }
  
  /**
   * process_one_work - process single work
   * @worker: self
   * @work: work to process
   *
   * Process @work.  This function contains all the logics necessary to
   * process a single work including synchronization against and
   * interaction with other workers on the same cpu, queueing and
   * flushing.  As long as context requirement is met, any worker can
   * call this function to process a work.
   *
   * CONTEXT:
   * spin_lock_irq(pool->lock) which is released and regrabbed.
   */
  static void process_one_work(struct worker *worker, struct work_struct *work)
  __releases(&pool->lock)
  __acquires(&pool->lock)
  {
  	struct pool_workqueue *pwq = get_work_pwq(work);
  	struct worker_pool *pool = worker->pool;
  	bool cpu_intensive = pwq->wq->flags & WQ_CPU_INTENSIVE;
  	int work_color;
  	struct worker *collision;
  #ifdef CONFIG_LOCKDEP
  	/*
  	 * It is permissible to free the struct work_struct from
  	 * inside the function that is called from it, this we need to
  	 * take into account for lockdep too.  To avoid bogus "held
  	 * lock freed" warnings as well as problems when looking into
  	 * work->lockdep_map, make a copy and use that here.
  	 */
  	struct lockdep_map lockdep_map;
  
  	lockdep_copy_map(&lockdep_map, &work->lockdep_map);
  #endif
  	/*
  	 * Ensure we're on the correct CPU.  DISASSOCIATED test is
  	 * necessary to avoid spurious warnings from rescuers servicing the
  	 * unbound or a disassociated pool.
  	 */
  	WARN_ON_ONCE(!(worker->flags & WORKER_UNBOUND) &&
  		     !(pool->flags & POOL_DISASSOCIATED) &&
  		     raw_smp_processor_id() != pool->cpu);
  
  	/*
  	 * A single work shouldn't be executed concurrently by
  	 * multiple workers on a single cpu.  Check whether anyone is
  	 * already processing the work.  If so, defer the work to the
  	 * currently executing one.
  	 */
  	collision = find_worker_executing_work(pool, work);
  	if (unlikely(collision)) {
  		move_linked_works(work, &collision->scheduled, NULL);
  		return;
  	}
  
  	/* claim and dequeue */
  	debug_work_deactivate(work);
  	hash_add(pool->busy_hash, &worker->hentry, (unsigned long)work);
  	worker->current_work = work;
  	worker->current_func = work->func;
  	worker->current_pwq = pwq;
  	work_color = get_work_color(work);
  
  	list_del_init(&work->entry);
  
  	/*
  	 * CPU intensive works don't participate in concurrency
  	 * management.  They're the scheduler's responsibility.
  	 */
  	if (unlikely(cpu_intensive))
  		worker_set_flags(worker, WORKER_CPU_INTENSIVE, true);
  
  	/*
  	 * Unbound pool isn't concurrency managed and work items should be
  	 * executed ASAP.  Wake up another worker if necessary.
  	 */
  	if ((worker->flags & WORKER_UNBOUND) && need_more_worker(pool))
  		wake_up_worker(pool);
  
  	/*
  	 * Record the last pool and clear PENDING which should be the last
  	 * update to @work.  Also, do this inside @pool->lock so that
  	 * PENDING and queued state changes happen together while IRQ is
  	 * disabled.
  	 */
  	set_work_pool_and_clear_pending(work, pool->id);
  
  	spin_unlock_irq(&pool->lock);
  
  	lock_map_acquire_read(&pwq->wq->lockdep_map);
  	lock_map_acquire(&lockdep_map);
  	trace_workqueue_execute_start(work);
  	worker->current_func(work);
  	/*
  	 * While we must be careful to not use "work" after this, the trace
  	 * point will only record its address.
  	 */
  	trace_workqueue_execute_end(work);
  	lock_map_release(&lockdep_map);
  	lock_map_release(&pwq->wq->lockdep_map);
  
  	if (unlikely(in_atomic() || lockdep_depth(current) > 0)) {
  		pr_err("BUG: workqueue leaked lock or atomic: %s/0x%08x/%d\n"
  		       "     last function: %pf\n",
  		       current->comm, preempt_count(), task_pid_nr(current),
  		       worker->current_func);
  		debug_show_held_locks(current);
  		dump_stack();
  	}
  
  	/*
  	 * The following prevents a kworker from hogging CPU on !PREEMPT
  	 * kernels, where a requeueing work item waiting for something to
  	 * happen could deadlock with stop_machine as such work item could
  	 * indefinitely requeue itself while all other CPUs are trapped in
  	 * stop_machine.
  	 */
  	cond_resched();
  
  	spin_lock_irq(&pool->lock);
  
  	/* clear cpu intensive status */
  	if (unlikely(cpu_intensive))
  		worker_clr_flags(worker, WORKER_CPU_INTENSIVE);
  
  	/* we're done with it, release */
  	hash_del(&worker->hentry);
  	worker->current_work = NULL;
  	worker->current_func = NULL;
  	worker->current_pwq = NULL;
  	worker->desc_valid = false;
  	pwq_dec_nr_in_flight(pwq, work_color);
  }
  
  /**
   * process_scheduled_works - process scheduled works
   * @worker: self
   *
   * Process all scheduled works.  Please note that the scheduled list
   * may change while processing a work, so this function repeatedly
   * fetches a work from the top and executes it.
   *
   * CONTEXT:
   * spin_lock_irq(pool->lock) which may be released and regrabbed
   * multiple times.
   */
  static void process_scheduled_works(struct worker *worker)
  {
  	while (!list_empty(&worker->scheduled)) {
  		struct work_struct *work = list_first_entry(&worker->scheduled,
  						struct work_struct, entry);
  		process_one_work(worker, work);
  	}
  }
  
  /**
   * worker_thread - the worker thread function
   * @__worker: self
   *
   * The worker thread function.  All workers belong to a worker_pool -
   * either a per-cpu one or dynamic unbound one.  These workers process all
   * work items regardless of their specific target workqueue.  The only
   * exception is work items which belong to workqueues with a rescuer which
   * will be explained in rescuer_thread().
   *
   * Return: 0
   */
  static int worker_thread(void *__worker)
  {
  	struct worker *worker = __worker;
  	struct worker_pool *pool = worker->pool;
  
  	/* tell the scheduler that this is a workqueue worker */
  	worker->task->flags |= PF_WQ_WORKER;
  woke_up:
  	spin_lock_irq(&pool->lock);
  
  	/* am I supposed to die? */
  	if (unlikely(worker->flags & WORKER_DIE)) {
  		spin_unlock_irq(&pool->lock);
  		WARN_ON_ONCE(!list_empty(&worker->entry));
  		worker->task->flags &= ~PF_WQ_WORKER;
  
  		set_task_comm(worker->task, "kworker/dying");
  		ida_simple_remove(&pool->worker_ida, worker->id);
  		worker_detach_from_pool(worker, pool);
  		kfree(worker);
  		return 0;
  	}
  
  	worker_leave_idle(worker);
  recheck:
  	/* no more worker necessary? */
  	if (!need_more_worker(pool))
  		goto sleep;
  
  	/* do we need to manage? */
  	if (unlikely(!may_start_working(pool)) && manage_workers(worker))
  		goto recheck;
  
  	/*
  	 * ->scheduled list can only be filled while a worker is
  	 * preparing to process a work or actually processing it.
  	 * Make sure nobody diddled with it while I was sleeping.
  	 */
  	WARN_ON_ONCE(!list_empty(&worker->scheduled));
  
  	/*
  	 * Finish PREP stage.  We're guaranteed to have at least one idle
  	 * worker or that someone else has already assumed the manager
  	 * role.  This is where @worker starts participating in concurrency
  	 * management if applicable and concurrency management is restored
  	 * after being rebound.  See rebind_workers() for details.
  	 */
  	worker_clr_flags(worker, WORKER_PREP | WORKER_REBOUND);
  
  	do {
  		struct work_struct *work =
  			list_first_entry(&pool->worklist,
  					 struct work_struct, entry);
  
  		if (likely(!(*work_data_bits(work) & WORK_STRUCT_LINKED))) {
  			/* optimization path, not strictly necessary */
  			process_one_work(worker, work);
  			if (unlikely(!list_empty(&worker->scheduled)))
  				process_scheduled_works(worker);
  		} else {
  			move_linked_works(work, &worker->scheduled, NULL);
  			process_scheduled_works(worker);
  		}
  	} while (keep_working(pool));
  
  	worker_set_flags(worker, WORKER_PREP, false);
  sleep:
  	/*
  	 * pool->lock is held and there's no work to process and no need to
  	 * manage, sleep.  Workers are woken up only while holding
  	 * pool->lock or from local cpu, so setting the current state
  	 * before releasing pool->lock is enough to prevent losing any
  	 * event.
  	 */
  	worker_enter_idle(worker);
  	__set_current_state(TASK_INTERRUPTIBLE);
  	spin_unlock_irq(&pool->lock);
  	schedule();
  	goto woke_up;
  }
  
  /**
   * rescuer_thread - the rescuer thread function
   * @__rescuer: self
   *
   * Workqueue rescuer thread function.  There's one rescuer for each
   * workqueue which has WQ_MEM_RECLAIM set.
   *
   * Regular work processing on a pool may block trying to create a new
   * worker which uses GFP_KERNEL allocation which has slight chance of
   * developing into deadlock if some works currently on the same queue
   * need to be processed to satisfy the GFP_KERNEL allocation.  This is
   * the problem rescuer solves.
   *
   * When such condition is possible, the pool summons rescuers of all
   * workqueues which have works queued on the pool and let them process
   * those works so that forward progress can be guaranteed.
   *
   * This should happen rarely.
   *
   * Return: 0
   */
  static int rescuer_thread(void *__rescuer)
  {
  	struct worker *rescuer = __rescuer;
  	struct workqueue_struct *wq = rescuer->rescue_wq;
  	struct list_head *scheduled = &rescuer->scheduled;
  	bool should_stop;
  
  	set_user_nice(current, RESCUER_NICE_LEVEL);
  
  	/*
  	 * Mark rescuer as worker too.  As WORKER_PREP is never cleared, it
  	 * doesn't participate in concurrency management.
  	 */
  	rescuer->task->flags |= PF_WQ_WORKER;
  repeat:
  	set_current_state(TASK_INTERRUPTIBLE);
  
  	/*
  	 * By the time the rescuer is requested to stop, the workqueue
  	 * shouldn't have any work pending, but @wq->maydays may still have
  	 * pwq(s) queued.  This can happen by non-rescuer workers consuming
  	 * all the work items before the rescuer got to them.  Go through
  	 * @wq->maydays processing before acting on should_stop so that the
  	 * list is always empty on exit.
  	 */
  	should_stop = kthread_should_stop();
  
  	/* see whether any pwq is asking for help */
  	spin_lock_irq(&wq_mayday_lock);
  
  	while (!list_empty(&wq->maydays)) {
  		struct pool_workqueue *pwq = list_first_entry(&wq->maydays,
  					struct pool_workqueue, mayday_node);
  		struct worker_pool *pool = pwq->pool;
  		struct work_struct *work, *n;
  
  		__set_current_state(TASK_RUNNING);
  		list_del_init(&pwq->mayday_node);
  
  		spin_unlock_irq(&wq_mayday_lock);
  
  		worker_attach_to_pool(rescuer, pool);
  
  		spin_lock_irq(&pool->lock);
  		rescuer->pool = pool;
  
  		/*
  		 * Slurp in all works issued via this workqueue and
  		 * process'em.
  		 */
  		WARN_ON_ONCE(!list_empty(&rescuer->scheduled));
  		list_for_each_entry_safe(work, n, &pool->worklist, entry)
  			if (get_work_pwq(work) == pwq)
  				move_linked_works(work, scheduled, &n);
  
  		process_scheduled_works(rescuer);
  		spin_unlock_irq(&pool->lock);
  
  		worker_detach_from_pool(rescuer, pool);
  
  		spin_lock_irq(&pool->lock);
  
  		/*
  		 * Put the reference grabbed by send_mayday().  @pool won't
  		 * go away while we're holding its lock.
  		 */
  		put_pwq(pwq);
  
  		/*
  		 * Leave this pool.  If keep_working() is %true, notify a
  		 * regular worker; otherwise, we end up with 0 concurrency
  		 * and stalling the execution.
  		 */
  		if (keep_working(pool))
  			wake_up_worker(pool);
  
  		rescuer->pool = NULL;
  		spin_unlock(&pool->lock);
  		spin_lock(&wq_mayday_lock);
  	}
  
  	spin_unlock_irq(&wq_mayday_lock);
  
  	if (should_stop) {
  		__set_current_state(TASK_RUNNING);
  		rescuer->task->flags &= ~PF_WQ_WORKER;
  		return 0;
  	}
  
  	/* rescuers should never participate in concurrency management */
  	WARN_ON_ONCE(!(rescuer->flags & WORKER_NOT_RUNNING));
  	schedule();
  	goto repeat;
  }
  
  struct wq_barrier {
  	struct work_struct	work;
  	struct completion	done;
  };
  
  static void wq_barrier_func(struct work_struct *work)
  {
  	struct wq_barrier *barr = container_of(work, struct wq_barrier, work);
  	complete(&barr->done);
  }
  
  /**
   * insert_wq_barrier - insert a barrier work
   * @pwq: pwq to insert barrier into
   * @barr: wq_barrier to insert
   * @target: target work to attach @barr to
   * @worker: worker currently executing @target, NULL if @target is not executing
   *
   * @barr is linked to @target such that @barr is completed only after
   * @target finishes execution.  Please note that the ordering
   * guarantee is observed only with respect to @target and on the local
   * cpu.
   *
   * Currently, a queued barrier can't be canceled.  This is because
   * try_to_grab_pending() can't determine whether the work to be
   * grabbed is at the head of the queue and thus can't clear LINKED
   * flag of the previous work while there must be a valid next work
   * after a work with LINKED flag set.
   *
   * Note that when @worker is non-NULL, @target may be modified
   * underneath us, so we can't reliably determine pwq from @target.
   *
   * CONTEXT:
   * spin_lock_irq(pool->lock).
   */
  static void insert_wq_barrier(struct pool_workqueue *pwq,
  			      struct wq_barrier *barr,
  			      struct work_struct *target, struct worker *worker)
  {
  	struct list_head *head;
  	unsigned int linked = 0;
  
  	/*
  	 * debugobject calls are safe here even with pool->lock locked
  	 * as we know for sure that this will not trigger any of the
  	 * checks and call back into the fixup functions where we
  	 * might deadlock.
  	 */
  	INIT_WORK_ONSTACK(&barr->work, wq_barrier_func);
  	__set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&barr->work));
  	init_completion(&barr->done);
  
  	/*
  	 * If @target is currently being executed, schedule the
  	 * barrier to the worker; otherwise, put it after @target.
  	 */
  	if (worker)
  		head = worker->scheduled.next;
  	else {
  		unsigned long *bits = work_data_bits(target);
  
  		head = target->entry.next;
  		/* there can already be other linked works, inherit and set */
  		linked = *bits & WORK_STRUCT_LINKED;
  		__set_bit(WORK_STRUCT_LINKED_BIT, bits);
  	}
  
  	debug_work_activate(&barr->work);
  	insert_work(pwq, &barr->work, head,
  		    work_color_to_flags(WORK_NO_COLOR) | linked);
  }
  
  /**
   * flush_workqueue_prep_pwqs - prepare pwqs for workqueue flushing
   * @wq: workqueue being flushed
   * @flush_color: new flush color, < 0 for no-op
   * @work_color: new work color, < 0 for no-op
   *
   * Prepare pwqs for workqueue flushing.
   *
   * If @flush_color is non-negative, flush_color on all pwqs should be
   * -1.  If no pwq has in-flight commands at the specified color, all
   * pwq->flush_color's stay at -1 and %false is returned.  If any pwq
   * has in flight commands, its pwq->flush_color is set to
   * @flush_color, @wq->nr_pwqs_to_flush is updated accordingly, pwq
   * wakeup logic is armed and %true is returned.
   *
   * The caller should have initialized @wq->first_flusher prior to
   * calling this function with non-negative @flush_color.  If
   * @flush_color is negative, no flush color update is done and %false
   * is returned.
   *
   * If @work_color is non-negative, all pwqs should have the same
   * work_color which is previous to @work_color and all will be
   * advanced to @work_color.
   *
   * CONTEXT:
   * mutex_lock(wq->mutex).
   *
   * Return:
   * %true if @flush_color >= 0 and there's something to flush.  %false
   * otherwise.
   */
  static bool flush_workqueue_prep_pwqs(struct workqueue_struct *wq,
  				      int flush_color, int work_color)
  {
  	bool wait = false;
  	struct pool_workqueue *pwq;
  
  	if (flush_color >= 0) {
  		WARN_ON_ONCE(atomic_read(&wq->nr_pwqs_to_flush));
  		atomic_set(&wq->nr_pwqs_to_flush, 1);
  	}
  
  	for_each_pwq(pwq, wq) {
  		struct worker_pool *pool = pwq->pool;
  
  		spin_lock_irq(&pool->lock);
  
  		if (flush_color >= 0) {
  			WARN_ON_ONCE(pwq->flush_color != -1);
  
  			if (pwq->nr_in_flight[flush_color]) {
  				pwq->flush_color = flush_color;
  				atomic_inc(&wq->nr_pwqs_to_flush);
  				wait = true;
  			}
  		}
  
  		if (work_color >= 0) {
  			WARN_ON_ONCE(work_color != work_next_color(pwq->work_color));
  			pwq->work_color = work_color;
  		}
  
  		spin_unlock_irq(&pool->lock);
  	}
  
  	if (flush_color >= 0 && atomic_dec_and_test(&wq->nr_pwqs_to_flush))
  		complete(&wq->first_flusher->done);
  
  	return wait;
  }
  
  /**
   * flush_workqueue - ensure that any scheduled work has run to completion.
   * @wq: workqueue to flush
   *
   * This function sleeps until all work items which were queued on entry
   * have finished execution, but it is not livelocked by new incoming ones.
   */
  void flush_workqueue(struct workqueue_struct *wq)
  {
  	struct wq_flusher this_flusher = {
  		.list = LIST_HEAD_INIT(this_flusher.list),
  		.flush_color = -1,
  		.done = COMPLETION_INITIALIZER_ONSTACK(this_flusher.done),
  	};
  	int next_color;
  
  	lock_map_acquire(&wq->lockdep_map);
  	lock_map_release(&wq->lockdep_map);
  
  	mutex_lock(&wq->mutex);
  
  	/*
  	 * Start-to-wait phase
  	 */
  	next_color = work_next_color(wq->work_color);
  
  	if (next_color != wq->flush_color) {
  		/*
  		 * Color space is not full.  The current work_color
  		 * becomes our flush_color and work_color is advanced
  		 * by one.
  		 */
  		WARN_ON_ONCE(!list_empty(&wq->flusher_overflow));
  		this_flusher.flush_color = wq->work_color;
  		wq->work_color = next_color;
  
  		if (!wq->first_flusher) {
  			/* no flush in progress, become the first flusher */
  			WARN_ON_ONCE(wq->flush_color != this_flusher.flush_color);
  
  			wq->first_flusher = &this_flusher;
  
  			if (!flush_workqueue_prep_pwqs(wq, wq->flush_color,
  						       wq->work_color)) {
  				/* nothing to flush, done */
  				wq->flush_color = next_color;
  				wq->first_flusher = NULL;
  				goto out_unlock;
  			}
  		} else {
  			/* wait in queue */
  			WARN_ON_ONCE(wq->flush_color == this_flusher.flush_color);
  			list_add_tail(&this_flusher.list, &wq->flusher_queue);
  			flush_workqueue_prep_pwqs(wq, -1, wq->work_color);
  		}
  	} else {
  		/*
  		 * Oops, color space is full, wait on overflow queue.
  		 * The next flush completion will assign us
  		 * flush_color and transfer to flusher_queue.
  		 */
  		list_add_tail(&this_flusher.list, &wq->flusher_overflow);
  	}
  
  	mutex_unlock(&wq->mutex);
  
  	wait_for_completion(&this_flusher.done);
  
  	/*
  	 * Wake-up-and-cascade phase
  	 *
  	 * First flushers are responsible for cascading flushes and
  	 * handling overflow.  Non-first flushers can simply return.
  	 */
  	if (wq->first_flusher != &this_flusher)
  		return;
  
  	mutex_lock(&wq->mutex);
  
  	/* we might have raced, check again with mutex held */
  	if (wq->first_flusher != &this_flusher)
  		goto out_unlock;
  
  	wq->first_flusher = NULL;
  
  	WARN_ON_ONCE(!list_empty(&this_flusher.list));
  	WARN_ON_ONCE(wq->flush_color != this_flusher.flush_color);
  
  	while (true) {
  		struct wq_flusher *next, *tmp;
  
  		/* complete all the flushers sharing the current flush color */
  		list_for_each_entry_safe(next, tmp, &wq->flusher_queue, list) {
  			if (next->flush_color != wq->flush_color)
  				break;
  			list_del_init(&next->list);
  			complete(&next->done);
  		}
  
  		WARN_ON_ONCE(!list_empty(&wq->flusher_overflow) &&
  			     wq->flush_color != work_next_color(wq->work_color));
  
  		/* this flush_color is finished, advance by one */
  		wq->flush_color = work_next_color(wq->flush_color);
  
  		/* one color has been freed, handle overflow queue */
  		if (!list_empty(&wq->flusher_overflow)) {
  			/*
  			 * Assign the same color to all overflowed
  			 * flushers, advance work_color and append to
  			 * flusher_queue.  This is the start-to-wait
  			 * phase for these overflowed flushers.
  			 */
  			list_for_each_entry(tmp, &wq->flusher_overflow, list)
  				tmp->flush_color = wq->work_color;
  
  			wq->work_color = work_next_color(wq->work_color);
  
  			list_splice_tail_init(&wq->flusher_overflow,
  					      &wq->flusher_queue);
  			flush_workqueue_prep_pwqs(wq, -1, wq->work_color);
  		}
  
  		if (list_empty(&wq->flusher_queue)) {
  			WARN_ON_ONCE(wq->flush_color != wq->work_color);
  			break;
  		}
  
  		/*
  		 * Need to flush more colors.  Make the next flusher
  		 * the new first flusher and arm pwqs.
  		 */
  		WARN_ON_ONCE(wq->flush_color == wq->work_color);
  		WARN_ON_ONCE(wq->flush_color != next->flush_color);
  
  		list_del_init(&next->list);
  		wq->first_flusher = next;
  
  		if (flush_workqueue_prep_pwqs(wq, wq->flush_color, -1))
  			break;
  
  		/*
  		 * Meh... this color is already done, clear first
  		 * flusher and repeat cascading.
  		 */
  		wq->first_flusher = NULL;
  	}
  
  out_unlock:
  	mutex_unlock(&wq->mutex);
  }
  EXPORT_SYMBOL_GPL(flush_workqueue);
  
  /**
   * drain_workqueue - drain a workqueue
   * @wq: workqueue to drain
   *
   * Wait until the workqueue becomes empty.  While draining is in progress,
   * only chain queueing is allowed.  IOW, only currently pending or running
   * work items on @wq can queue further work items on it.  @wq is flushed
   * repeatedly until it becomes empty.  The number of flushing is detemined
   * by the depth of chaining and should be relatively short.  Whine if it
   * takes too long.
   */
  void drain_workqueue(struct workqueue_struct *wq)
  {
  	unsigned int flush_cnt = 0;
  	struct pool_workqueue *pwq;
  
  	/*
  	 * __queue_work() needs to test whether there are drainers, is much
  	 * hotter than drain_workqueue() and already looks at @wq->flags.
  	 * Use __WQ_DRAINING so that queue doesn't have to check nr_drainers.
  	 */
  	mutex_lock(&wq->mutex);
  	if (!wq->nr_drainers++)
  		wq->flags |= __WQ_DRAINING;
  	mutex_unlock(&wq->mutex);
  reflush:
  	flush_workqueue(wq);
  
  	mutex_lock(&wq->mutex);
  
  	for_each_pwq(pwq, wq) {
  		bool drained;
  
  		spin_lock_irq(&pwq->pool->lock);
  		drained = !pwq->nr_active && list_empty(&pwq->delayed_works);
  		spin_unlock_irq(&pwq->pool->lock);
  
  		if (drained)
  			continue;
  
  		if (++flush_cnt == 10 ||
  		    (flush_cnt % 100 == 0 && flush_cnt <= 1000))
  			pr_warn("workqueue %s: drain_workqueue() isn't complete after %u tries\n",
  				wq->name, flush_cnt);
  
  		mutex_unlock(&wq->mutex);
  		goto reflush;
  	}
  
  	if (!--wq->nr_drainers)
  		wq->flags &= ~__WQ_DRAINING;
  	mutex_unlock(&wq->mutex);
  }
  EXPORT_SYMBOL_GPL(drain_workqueue);
  
  static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr)
  {
  	struct worker *worker = NULL;
  	struct worker_pool *pool;
  	struct pool_workqueue *pwq;
  
  	might_sleep();
  
  	local_irq_disable();
  	pool = get_work_pool(work);
  	if (!pool) {
  		local_irq_enable();
  		return false;
  	}
  
  	spin_lock(&pool->lock);
  	/* see the comment in try_to_grab_pending() with the same code */
  	pwq = get_work_pwq(work);
  	if (pwq) {
  		if (unlikely(pwq->pool != pool))
  			goto already_gone;
  	} else {
  		worker = find_worker_executing_work(pool, work);
  		if (!worker)
  			goto already_gone;
  		pwq = worker->current_pwq;
  	}
  
  	insert_wq_barrier(pwq, barr, work, worker);
  	spin_unlock_irq(&pool->lock);
  
  	/*
  	 * If @max_active is 1 or rescuer is in use, flushing another work
  	 * item on the same workqueue may lead to deadlock.  Make sure the
  	 * flusher is not running on the same workqueue by verifying write
  	 * access.
  	 */
  	if (pwq->wq->saved_max_active == 1 || pwq->wq->rescuer)
  		lock_map_acquire(&pwq->wq->lockdep_map);
  	else
  		lock_map_acquire_read(&pwq->wq->lockdep_map);
  	lock_map_release(&pwq->wq->lockdep_map);
  
  	return true;
  already_gone:
  	spin_unlock_irq(&pool->lock);
  	return false;
  }
  
  /**
   * flush_work - wait for a work to finish executing the last queueing instance
   * @work: the work to flush
   *
   * Wait until @work has finished execution.  @work is guaranteed to be idle
   * on return if it hasn't been requeued since flush started.
   *
   * Return:
   * %true if flush_work() waited for the work to finish execution,
   * %false if it was already idle.
   */
  bool flush_work(struct work_struct *work)
  {
  	struct wq_barrier barr;
  
  	lock_map_acquire(&work->lockdep_map);
  	lock_map_release(&work->lockdep_map);
  
  	if (start_flush_work(work, &barr)) {
  		wait_for_completion(&barr.done);
  		destroy_work_on_stack(&barr.work);
  		return true;
  	} else {
  		return false;
  	}
  }
  EXPORT_SYMBOL_GPL(flush_work);
  
  static bool __cancel_work_timer(struct work_struct *work, bool is_dwork)
  {
  	unsigned long flags;
  	int ret;
  
  	do {
  		ret = try_to_grab_pending(work, is_dwork, &flags);
  		/*
  		 * If someone else is canceling, wait for the same event it
  		 * would be waiting for before retrying.
  		 */
  		if (unlikely(ret == -ENOENT))
  			flush_work(work);
  	} while (unlikely(ret < 0));
  
  	/* tell other tasks trying to grab @work to back off */
  	mark_work_canceling(work);
  	local_irq_restore(flags);
  
  	flush_work(work);
  	clear_work_data(work);
  	return ret;
  }
  
  /**
   * cancel_work_sync - cancel a work and wait for it to finish
   * @work: the work to cancel
   *
   * Cancel @work and wait for its execution to finish.  This function
   * can be used even if the work re-queues itself or migrates to
   * another workqueue.  On return from this function, @work is
   * guaranteed to be not pending or executing on any CPU.
   *
   * cancel_work_sync(&delayed_work->work) must not be used for
   * delayed_work's.  Use cancel_delayed_work_sync() instead.
   *
   * The caller must ensure that the workqueue on which @work was last
   * queued can't be destroyed before this function returns.
   *
   * Return:
   * %true if @work was pending, %false otherwise.
   */
  bool cancel_work_sync(struct work_struct *work)
  {
  	return __cancel_work_timer(work, false);
  }
  EXPORT_SYMBOL_GPL(cancel_work_sync);
  
  /**
   * flush_delayed_work - wait for a dwork to finish executing the last queueing
   * @dwork: the delayed work to flush
   *
   * Delayed timer is cancelled and the pending work is queued for
   * immediate execution.  Like flush_work(), this function only
   * considers the last queueing instance of @dwork.
   *
   * Return:
   * %true if flush_work() waited for the work to finish execution,
   * %false if it was already idle.
   */
  bool flush_delayed_work(struct delayed_work *dwork)
  {
  	local_irq_disable();
  	if (del_timer_sync(&dwork->timer))
  		__queue_work(dwork->cpu, dwork->wq, &dwork->work);
  	local_irq_enable();
  	return flush_work(&dwork->work);
  }
  EXPORT_SYMBOL(flush_delayed_work);
  
  /**
   * cancel_delayed_work - cancel a delayed work
   * @dwork: delayed_work to cancel
   *
   * Kill off a pending delayed_work.
   *
   * Return: %true if @dwork was pending and canceled; %false if it wasn't
   * pending.
   *
   * Note:
   * The work callback function may still be running on return, unless
   * it returns %true and the work doesn't re-arm itself.  Explicitly flush or
   * use cancel_delayed_work_sync() to wait on it.
   *
   * This function is safe to call from any context including IRQ handler.
   */
  bool cancel_delayed_work(struct delayed_work *dwork)
  {
  	unsigned long flags;
  	int ret;
  
  	do {
  		ret = try_to_grab_pending(&dwork->work, true, &flags);
  	} while (unlikely(ret == -EAGAIN));
  
  	if (unlikely(ret < 0))
  		return false;
  
  	set_work_pool_and_clear_pending(&dwork->work,
  					get_work_pool_id(&dwork->work));
  	local_irq_restore(flags);
  	return ret;
  }
  EXPORT_SYMBOL(cancel_delayed_work);
  
  /**
   * cancel_delayed_work_sync - cancel a delayed work and wait for it to finish
   * @dwork: the delayed work cancel
   *
   * This is cancel_work_sync() for delayed works.
   *
   * Return:
   * %true if @dwork was pending, %false otherwise.
   */
  bool cancel_delayed_work_sync(struct delayed_work *dwork)
  {
  	return __cancel_work_timer(&dwork->work, true);
  }
  EXPORT_SYMBOL(cancel_delayed_work_sync);
  
  /**
   * schedule_on_each_cpu - execute a function synchronously on each online CPU
   * @func: the function to call
   *
   * schedule_on_each_cpu() executes @func on each online CPU using the
   * system workqueue and blocks until all CPUs have completed.
   * schedule_on_each_cpu() is very slow.
   *
   * Return:
   * 0 on success, -errno on failure.
   */
  int schedule_on_each_cpu(work_func_t func)
  {
  	int cpu;
  	struct work_struct __percpu *works;
  
  	works = alloc_percpu(struct work_struct);
  	if (!works)
  		return -ENOMEM;
  
  	get_online_cpus();
  
  	for_each_online_cpu(cpu) {
  		struct work_struct *work = per_cpu_ptr(works, cpu);
  
  		INIT_WORK(work, func);
  		schedule_work_on(cpu, work);
  	}
  
  	for_each_online_cpu(cpu)
  		flush_work(per_cpu_ptr(works, cpu));
  
  	put_online_cpus();
  	free_percpu(works);
  	return 0;
  }
  
  /**
   * flush_scheduled_work - ensure that any scheduled work has run to completion.
   *
   * Forces execution of the kernel-global workqueue and blocks until its
   * completion.
   *
   * Think twice before calling this function!  It's very easy to get into
   * trouble if you don't take great care.  Either of the following situations
   * will lead to deadlock:
   *
   *	One of the work items currently on the workqueue needs to acquire
   *	a lock held by your code or its caller.
   *
   *	Your code is running in the context of a work routine.
   *
   * They will be detected by lockdep when they occur, but the first might not
   * occur very often.  It depends on what work items are on the workqueue and
   * what locks they need, which you have no control over.
   *
   * In most situations flushing the entire workqueue is overkill; you merely
   * need to know that a particular work item isn't queued and isn't running.
   * In such cases you should use cancel_delayed_work_sync() or
   * cancel_work_sync() instead.
   */
  void flush_scheduled_work(void)
  {
  	flush_workqueue(system_wq);
  }
  EXPORT_SYMBOL(flush_scheduled_work);
  
  /**
   * execute_in_process_context - reliably execute the routine with user context
   * @fn:		the function to execute
   * @ew:		guaranteed storage for the execute work structure (must
   *		be available when the work executes)
   *
   * Executes the function immediately if process context is available,
   * otherwise schedules the function for delayed execution.
   *
   * Return:	0 - function was executed
   *		1 - function was scheduled for execution
   */
  int execute_in_process_context(work_func_t fn, struct execute_work *ew)
  {
  	if (!in_interrupt()) {
  		fn(&ew->work);
  		return 0;
  	}
  
  	INIT_WORK(&ew->work, fn);
  	schedule_work(&ew->work);
  
  	return 1;
  }
  EXPORT_SYMBOL_GPL(execute_in_process_context);
  
  #ifdef CONFIG_SYSFS
  /*
   * Workqueues with WQ_SYSFS flag set is visible to userland via
   * /sys/bus/workqueue/devices/WQ_NAME.  All visible workqueues have the
   * following attributes.
   *
   *  per_cpu	RO bool	: whether the workqueue is per-cpu or unbound
   *  max_active	RW int	: maximum number of in-flight work items
   *
   * Unbound workqueues have the following extra attributes.
   *
   *  id		RO int	: the associated pool ID
   *  nice	RW int	: nice value of the workers
   *  cpumask	RW mask	: bitmask of allowed CPUs for the workers
   */
  struct wq_device {
  	struct workqueue_struct		*wq;
  	struct device			dev;
  };
  
  static struct workqueue_struct *dev_to_wq(struct device *dev)
  {
  	struct wq_device *wq_dev = container_of(dev, struct wq_device, dev);
  
  	return wq_dev->wq;
  }
  
  static ssize_t per_cpu_show(struct device *dev, struct device_attribute *attr,
  			    char *buf)
  {
  	struct workqueue_struct *wq = dev_to_wq(dev);
  
  	return scnprintf(buf, PAGE_SIZE, "%d\n", (bool)!(wq->flags & WQ_UNBOUND));
  }
  static DEVICE_ATTR_RO(per_cpu);
  
  static ssize_t max_active_show(struct device *dev,
  			       struct device_attribute *attr, char *buf)
  {
  	struct workqueue_struct *wq = dev_to_wq(dev);
  
  	return scnprintf(buf, PAGE_SIZE, "%d\n", wq->saved_max_active);
  }
  
  static ssize_t max_active_store(struct device *dev,
  				struct device_attribute *attr, const char *buf,
  				size_t count)
  {
  	struct workqueue_struct *wq = dev_to_wq(dev);
  	int val;
  
  	if (sscanf(buf, "%d", &val) != 1 || val <= 0)
  		return -EINVAL;
  
  	workqueue_set_max_active(wq, val);
  	return count;
  }
  static DEVICE_ATTR_RW(max_active);
  
  static struct attribute *wq_sysfs_attrs[] = {
  	&dev_attr_per_cpu.attr,
  	&dev_attr_max_active.attr,
  	NULL,
  };
  ATTRIBUTE_GROUPS(wq_sysfs);
  
  static ssize_t wq_pool_ids_show(struct device *dev,
  				struct device_attribute *attr, char *buf)
  {
  	struct workqueue_struct *wq = dev_to_wq(dev);
  	const char *delim = "";
  	int node, written = 0;
  
  	rcu_read_lock_sched();
  	for_each_node(node) {
  		written += scnprintf(buf + written, PAGE_SIZE - written,
  				     "%s%d:%d", delim, node,
  				     unbound_pwq_by_node(wq, node)->pool->id);
  		delim = " ";
  	}
  	written += scnprintf(buf + written, PAGE_SIZE - written, "\n");
  	rcu_read_unlock_sched();
  
  	return written;
  }
  
  static ssize_t wq_nice_show(struct device *dev, struct device_attribute *attr,
  			    char *buf)
  {
  	struct workqueue_struct *wq = dev_to_wq(dev);
  	int written;
  
  	mutex_lock(&wq->mutex);
  	written = scnprintf(buf, PAGE_SIZE, "%d\n", wq->unbound_attrs->nice);
  	mutex_unlock(&wq->mutex);
  
  	return written;
  }
  
  /* prepare workqueue_attrs for sysfs store operations */
  static struct workqueue_attrs *wq_sysfs_prep_attrs(struct workqueue_struct *wq)
  {
  	struct workqueue_attrs *attrs;
  
  	attrs = alloc_workqueue_attrs(GFP_KERNEL);
  	if (!attrs)
  		return NULL;
  
  	mutex_lock(&wq->mutex);
  	copy_workqueue_attrs(attrs, wq->unbound_attrs);
  	mutex_unlock(&wq->mutex);
  	return attrs;
  }
  
  static ssize_t wq_nice_store(struct device *dev, struct device_attribute *attr,
  			     const char *buf, size_t count)
  {
  	struct workqueue_struct *wq = dev_to_wq(dev);
  	struct workqueue_attrs *attrs;
  	int ret;
  
  	attrs = wq_sysfs_prep_attrs(wq);
  	if (!attrs)
  		return -ENOMEM;
  
  	if (sscanf(buf, "%d", &attrs->nice) == 1 &&
  	    attrs->nice >= MIN_NICE && attrs->nice <= MAX_NICE)
  		ret = apply_workqueue_attrs(wq, attrs);
  	else
  		ret = -EINVAL;
  
  	free_workqueue_attrs(attrs);
  	return ret ?: count;
  }
  
  static ssize_t wq_cpumask_show(struct device *dev,
  			       struct device_attribute *attr, char *buf)
  {
  	struct workqueue_struct *wq = dev_to_wq(dev);
  	int written;
  
  	mutex_lock(&wq->mutex);
  	written = cpumask_scnprintf(buf, PAGE_SIZE, wq->unbound_attrs->cpumask);
  	mutex_unlock(&wq->mutex);
  
  	written += scnprintf(buf + written, PAGE_SIZE - written, "\n");
  	return written;
  }
  
  static ssize_t wq_cpumask_store(struct device *dev,
  				struct device_attribute *attr,
  				const char *buf, size_t count)
  {
  	struct workqueue_struct *wq = dev_to_wq(dev);
  	struct workqueue_attrs *attrs;
  	int ret;
  
  	attrs = wq_sysfs_prep_attrs(wq);
  	if (!attrs)
  		return -ENOMEM;
  
  	ret = cpumask_parse(buf, attrs->cpumask);
  	if (!ret)
  		ret = apply_workqueue_attrs(wq, attrs);
  
  	free_workqueue_attrs(attrs);
  	return ret ?: count;
  }
  
  static ssize_t wq_numa_show(struct device *dev, struct device_attribute *attr,
  			    char *buf)
  {
  	struct workqueue_struct *wq = dev_to_wq(dev);
  	int written;
  
  	mutex_lock(&wq->mutex);
  	written = scnprintf(buf, PAGE_SIZE, "%d\n",
  			    !wq->unbound_attrs->no_numa);
  	mutex_unlock(&wq->mutex);
  
  	return written;
  }
  
  static ssize_t wq_numa_store(struct device *dev, struct device_attribute *attr,
  			     const char *buf, size_t count)
  {
  	struct workqueue_struct *wq = dev_to_wq(dev);
  	struct workqueue_attrs *attrs;
  	int v, ret;
  
  	attrs = wq_sysfs_prep_attrs(wq);
  	if (!attrs)
  		return -ENOMEM;
  
  	ret = -EINVAL;
  	if (sscanf(buf, "%d", &v) == 1) {
  		attrs->no_numa = !v;
  		ret = apply_workqueue_attrs(wq, attrs);
  	}
  
  	free_workqueue_attrs(attrs);
  	return ret ?: count;
  }
  
  static struct device_attribute wq_sysfs_unbound_attrs[] = {
  	__ATTR(pool_ids, 0444, wq_pool_ids_show, NULL),
  	__ATTR(nice, 0644, wq_nice_show, wq_nice_store),
  	__ATTR(cpumask, 0644, wq_cpumask_show, wq_cpumask_store),
  	__ATTR(numa, 0644, wq_numa_show, wq_numa_store),
  	__ATTR_NULL,
  };
  
  static struct bus_type wq_subsys = {
  	.name				= "workqueue",
  	.dev_groups			= wq_sysfs_groups,
  };
  
  static int __init wq_sysfs_init(void)
  {
  	return subsys_virtual_register(&wq_subsys, NULL);
  }
  core_initcall(wq_sysfs_init);
  
  static void wq_device_release(struct device *dev)
  {
  	struct wq_device *wq_dev = container_of(dev, struct wq_device, dev);
  
  	kfree(wq_dev);
  }
  
  /**
   * workqueue_sysfs_register - make a workqueue visible in sysfs
   * @wq: the workqueue to register
   *
   * Expose @wq in sysfs under /sys/bus/workqueue/devices.
   * alloc_workqueue*() automatically calls this function if WQ_SYSFS is set
   * which is the preferred method.
   *
   * Workqueue user should use this function directly iff it wants to apply
   * workqueue_attrs before making the workqueue visible in sysfs; otherwise,
   * apply_workqueue_attrs() may race against userland updating the
   * attributes.
   *
   * Return: 0 on success, -errno on failure.
   */
  int workqueue_sysfs_register(struct workqueue_struct *wq)
  {
  	struct wq_device *wq_dev;
  	int ret;
  
  	/*
  	 * Adjusting max_active or creating new pwqs by applyting
  	 * attributes breaks ordering guarantee.  Disallow exposing ordered
  	 * workqueues.
  	 */
  	if (WARN_ON(wq->flags & __WQ_ORDERED))
  		return -EINVAL;
  
  	wq->wq_dev = wq_dev = kzalloc(sizeof(*wq_dev), GFP_KERNEL);
  	if (!wq_dev)
  		return -ENOMEM;
  
  	wq_dev->wq = wq;
  	wq_dev->dev.bus = &wq_subsys;
  	wq_dev->dev.init_name = wq->name;
  	wq_dev->dev.release = wq_device_release;
  
  	/*
  	 * unbound_attrs are created separately.  Suppress uevent until
  	 * everything is ready.
  	 */
  	dev_set_uevent_suppress(&wq_dev->dev, true);
  
  	ret = device_register(&wq_dev->dev);
  	if (ret) {
  		kfree(wq_dev);
  		wq->wq_dev = NULL;
  		return ret;
  	}
  
  	if (wq->flags & WQ_UNBOUND) {
  		struct device_attribute *attr;
  
  		for (attr = wq_sysfs_unbound_attrs; attr->attr.name; attr++) {
  			ret = device_create_file(&wq_dev->dev, attr);
  			if (ret) {
  				device_unregister(&wq_dev->dev);
  				wq->wq_dev = NULL;
  				return ret;
  			}
  		}
  	}
  
  	dev_set_uevent_suppress(&wq_dev->dev, false);
  	kobject_uevent(&wq_dev->dev.kobj, KOBJ_ADD);
  	return 0;
  }
  
  /**
   * workqueue_sysfs_unregister - undo workqueue_sysfs_register()
   * @wq: the workqueue to unregister
   *
   * If @wq is registered to sysfs by workqueue_sysfs_register(), unregister.
   */
  static void workqueue_sysfs_unregister(struct workqueue_struct *wq)
  {
  	struct wq_device *wq_dev = wq->wq_dev;
  
  	if (!wq->wq_dev)
  		return;
  
  	wq->wq_dev = NULL;
  	device_unregister(&wq_dev->dev);
  }
  #else	/* CONFIG_SYSFS */
  static void workqueue_sysfs_unregister(struct workqueue_struct *wq)	{ }
  #endif	/* CONFIG_SYSFS */
  
  /**
   * free_workqueue_attrs - free a workqueue_attrs
   * @attrs: workqueue_attrs to free
   *
   * Undo alloc_workqueue_attrs().
   */
  void free_workqueue_attrs(struct workqueue_attrs *attrs)
  {
  	if (attrs) {
  		free_cpumask_var(attrs->cpumask);
  		kfree(attrs);
  	}
  }
  
  /**
   * alloc_workqueue_attrs - allocate a workqueue_attrs
   * @gfp_mask: allocation mask to use
   *
   * Allocate a new workqueue_attrs, initialize with default settings and
   * return it.
   *
   * Return: The allocated new workqueue_attr on success. %NULL on failure.
   */
  struct workqueue_attrs *alloc_workqueue_attrs(gfp_t gfp_mask)
  {
  	struct workqueue_attrs *attrs;
  
  	attrs = kzalloc(sizeof(*attrs), gfp_mask);
  	if (!attrs)
  		goto fail;
  	if (!alloc_cpumask_var(&attrs->cpumask, gfp_mask))
  		goto fail;
  
  	cpumask_copy(attrs->cpumask, cpu_possible_mask);
  	return attrs;
  fail:
  	free_workqueue_attrs(attrs);
  	return NULL;
  }
  
  static void copy_workqueue_attrs(struct workqueue_attrs *to,
  				 const struct workqueue_attrs *from)
  {
  	to->nice = from->nice;
  	cpumask_copy(to->cpumask, from->cpumask);
  	/*
  	 * Unlike hash and equality test, this function doesn't ignore
  	 * ->no_numa as it is used for both pool and wq attrs.  Instead,
  	 * get_unbound_pool() explicitly clears ->no_numa after copying.
  	 */
  	to->no_numa = from->no_numa;
  }
  
  /* hash value of the content of @attr */
  static u32 wqattrs_hash(const struct workqueue_attrs *attrs)
  {
  	u32 hash = 0;
  
  	hash = jhash_1word(attrs->nice, hash);
  	hash = jhash(cpumask_bits(attrs->cpumask),
  		     BITS_TO_LONGS(nr_cpumask_bits) * sizeof(long), hash);
  	return hash;
  }
  
  /* content equality test */
  static bool wqattrs_equal(const struct workqueue_attrs *a,
  			  const struct workqueue_attrs *b)
  {
  	if (a->nice != b->nice)
  		return false;
  	if (!cpumask_equal(a->cpumask, b->cpumask))
  		return false;
  	return true;
  }
  
  /**
   * init_worker_pool - initialize a newly zalloc'd worker_pool
   * @pool: worker_pool to initialize
   *
   * Initiailize a newly zalloc'd @pool.  It also allocates @pool->attrs.
   *
   * Return: 0 on success, -errno on failure.  Even on failure, all fields
   * inside @pool proper are initialized and put_unbound_pool() can be called
   * on @pool safely to release it.
   */
  static int init_worker_pool(struct worker_pool *pool)
  {
  	spin_lock_init(&pool->lock);
  	pool->id = -1;
  	pool->cpu = -1;
  	pool->node = NUMA_NO_NODE;
  	pool->flags |= POOL_DISASSOCIATED;
  	INIT_LIST_HEAD(&pool->worklist);
  	INIT_LIST_HEAD(&pool->idle_list);
  	hash_init(pool->busy_hash);
  
  	init_timer_deferrable(&pool->idle_timer);
  	pool->idle_timer.function = idle_worker_timeout;
  	pool->idle_timer.data = (unsigned long)pool;
  
  	setup_timer(&pool->mayday_timer, pool_mayday_timeout,
  		    (unsigned long)pool);
  
  	mutex_init(&pool->manager_arb);
  	mutex_init(&pool->attach_mutex);
  	INIT_LIST_HEAD(&pool->workers);
  
  	ida_init(&pool->worker_ida);
  	INIT_HLIST_NODE(&pool->hash_node);
  	pool->refcnt = 1;
  
  	/* shouldn't fail above this point */
  	pool->attrs = alloc_workqueue_attrs(GFP_KERNEL);
  	if (!pool->attrs)
  		return -ENOMEM;
  	return 0;
  }
  
  static void rcu_free_pool(struct rcu_head *rcu)
  {
  	struct worker_pool *pool = container_of(rcu, struct worker_pool, rcu);
  
  	ida_destroy(&pool->worker_ida);
  	free_workqueue_attrs(pool->attrs);
  	kfree(pool);
  }
  
  /**
   * put_unbound_pool - put a worker_pool
   * @pool: worker_pool to put
   *
   * Put @pool.  If its refcnt reaches zero, it gets destroyed in sched-RCU
   * safe manner.  get_unbound_pool() calls this function on its failure path
   * and this function should be able to release pools which went through,
   * successfully or not, init_worker_pool().
   *
   * Should be called with wq_pool_mutex held.
   */
  static void put_unbound_pool(struct worker_pool *pool)
  {
  	DECLARE_COMPLETION_ONSTACK(detach_completion);
  	struct worker *worker;
  
  	lockdep_assert_held(&wq_pool_mutex);
  
  	if (--pool->refcnt)
  		return;
  
  	/* sanity checks */
  	if (WARN_ON(!(pool->flags & POOL_DISASSOCIATED)) ||
  	    WARN_ON(!list_empty(&pool->worklist)))
  		return;
  
  	/* release id and unhash */
  	if (pool->id >= 0)
  		idr_remove(&worker_pool_idr, pool->id);
  	hash_del(&pool->hash_node);
  
  	/*
  	 * Become the manager and destroy all workers.  Grabbing
  	 * manager_arb prevents @pool's workers from blocking on
  	 * attach_mutex.
  	 */
  	mutex_lock(&pool->manager_arb);
  
  	spin_lock_irq(&pool->lock);
  	while ((worker = first_idle_worker(pool)))
  		destroy_worker(worker);
  	WARN_ON(pool->nr_workers || pool->nr_idle);
  	spin_unlock_irq(&pool->lock);
  
  	mutex_lock(&pool->attach_mutex);
  	if (!list_empty(&pool->workers))
  		pool->detach_completion = &detach_completion;
  	mutex_unlock(&pool->attach_mutex);
  
  	if (pool->detach_completion)
  		wait_for_completion(pool->detach_completion);
  
  	mutex_unlock(&pool->manager_arb);
  
  	/* shut down the timers */
  	del_timer_sync(&pool->idle_timer);
  	del_timer_sync(&pool->mayday_timer);
  
  	/* sched-RCU protected to allow dereferences from get_work_pool() */
  	call_rcu_sched(&pool->rcu, rcu_free_pool);
  }
  
  /**
   * get_unbound_pool - get a worker_pool with the specified attributes
   * @attrs: the attributes of the worker_pool to get
   *
   * Obtain a worker_pool which has the same attributes as @attrs, bump the
   * reference count and return it.  If there already is a matching
   * worker_pool, it will be used; otherwise, this function attempts to
   * create a new one.
   *
   * Should be called with wq_pool_mutex held.
   *
   * Return: On success, a worker_pool with the same attributes as @attrs.
   * On failure, %NULL.
   */
  static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
  {
  	u32 hash = wqattrs_hash(attrs);
  	struct worker_pool *pool;
  	int node;
  
  	lockdep_assert_held(&wq_pool_mutex);
  
  	/* do we already have a matching pool? */
  	hash_for_each_possible(unbound_pool_hash, pool, hash_node, hash) {
  		if (wqattrs_equal(pool->attrs, attrs)) {
  			pool->refcnt++;
  			goto out_unlock;
  		}
  	}
  
  	/* nope, create a new one */
  	pool = kzalloc(sizeof(*pool), GFP_KERNEL);
  	if (!pool || init_worker_pool(pool) < 0)
  		goto fail;
  
  	lockdep_set_subclass(&pool->lock, 1);	/* see put_pwq() */
  	copy_workqueue_attrs(pool->attrs, attrs);
  
  	/*
  	 * no_numa isn't a worker_pool attribute, always clear it.  See
  	 * 'struct workqueue_attrs' comments for detail.
  	 */
  	pool->attrs->no_numa = false;
  
  	/* if cpumask is contained inside a NUMA node, we belong to that node */
  	if (wq_numa_enabled) {
  		for_each_node(node) {
  			if (cpumask_subset(pool->attrs->cpumask,
  					   wq_numa_possible_cpumask[node])) {
  				pool->node = node;
  				break;
  			}
  		}
  	}
  
  	if (worker_pool_assign_id(pool) < 0)
  		goto fail;
  
  	/* create and start the initial worker */
  	if (create_and_start_worker(pool) < 0)
  		goto fail;
  
  	/* install */
  	hash_add(unbound_pool_hash, &pool->hash_node, hash);
  out_unlock:
  	return pool;
  fail:
  	if (pool)
  		put_unbound_pool(pool);
  	return NULL;
  }
  
  static void rcu_free_pwq(struct rcu_head *rcu)
  {
  	kmem_cache_free(pwq_cache,
  			container_of(rcu, struct pool_workqueue, rcu));
  }
  
  /*
   * Scheduled on system_wq by put_pwq() when an unbound pwq hits zero refcnt
   * and needs to be destroyed.
   */
  static void pwq_unbound_release_workfn(struct work_struct *work)
  {
  	struct pool_workqueue *pwq = container_of(work, struct pool_workqueue,
  						  unbound_release_work);
  	struct workqueue_struct *wq = pwq->wq;
  	struct worker_pool *pool = pwq->pool;
  	bool is_last;
  
  	if (WARN_ON_ONCE(!(wq->flags & WQ_UNBOUND)))
  		return;
  
  	/*
  	 * Unlink @pwq.  Synchronization against wq->mutex isn't strictly
  	 * necessary on release but do it anyway.  It's easier to verify
  	 * and consistent with the linking path.
  	 */
  	mutex_lock(&wq->mutex);
  	list_del_rcu(&pwq->pwqs_node);
  	is_last = list_empty(&wq->pwqs);
  	mutex_unlock(&wq->mutex);
  
  	mutex_lock(&wq_pool_mutex);
  	put_unbound_pool(pool);
  	mutex_unlock(&wq_pool_mutex);
  
  	call_rcu_sched(&pwq->rcu, rcu_free_pwq);
  
  	/*
  	 * If we're the last pwq going away, @wq is already dead and no one
  	 * is gonna access it anymore.  Free it.
  	 */
  	if (is_last) {
  		free_workqueue_attrs(wq->unbound_attrs);
  		kfree(wq);
  	}
  }
  
  /**
   * pwq_adjust_max_active - update a pwq's max_active to the current setting
   * @pwq: target pool_workqueue
   *
   * If @pwq isn't freezing, set @pwq->max_active to the associated
   * workqueue's saved_max_active and activate delayed work items
   * accordingly.  If @pwq is freezing, clear @pwq->max_active to zero.
   */
  static void pwq_adjust_max_active(struct pool_workqueue *pwq)
  {
  	struct workqueue_struct *wq = pwq->wq;
  	bool freezable = wq->flags & WQ_FREEZABLE;
  
  	/* for @wq->saved_max_active */
  	lockdep_assert_held(&wq->mutex);
  
  	/* fast exit for non-freezable wqs */
  	if (!freezable && pwq->max_active == wq->saved_max_active)
  		return;
  
  	spin_lock_irq(&pwq->pool->lock);
  
  	/*
  	 * During [un]freezing, the caller is responsible for ensuring that
  	 * this function is called at least once after @workqueue_freezing
  	 * is updated and visible.
  	 */
  	if (!freezable || !workqueue_freezing) {
  		pwq->max_active = wq->saved_max_active;
  
  		while (!list_empty(&pwq->delayed_works) &&
  		       pwq->nr_active < pwq->max_active)
  			pwq_activate_first_delayed(pwq);
  
  		/*
  		 * Need to kick a worker after thawed or an unbound wq's
  		 * max_active is bumped.  It's a slow path.  Do it always.
  		 */
  		wake_up_worker(pwq->pool);
  	} else {
  		pwq->max_active = 0;
  	}
  
  	spin_unlock_irq(&pwq->pool->lock);
  }
  
  /* initialize newly alloced @pwq which is associated with @wq and @pool */
  static void init_pwq(struct pool_workqueue *pwq, struct workqueue_struct *wq,
  		     struct worker_pool *pool)
  {
  	BUG_ON((unsigned long)pwq & WORK_STRUCT_FLAG_MASK);
  
  	memset(pwq, 0, sizeof(*pwq));
  
  	pwq->pool = pool;
  	pwq->wq = wq;
  	pwq->flush_color = -1;
  	pwq->refcnt = 1;
  	INIT_LIST_HEAD(&pwq->delayed_works);
  	INIT_LIST_HEAD(&pwq->pwqs_node);
  	INIT_LIST_HEAD(&pwq->mayday_node);
  	INIT_WORK(&pwq->unbound_release_work, pwq_unbound_release_workfn);
  }
  
  /* sync @pwq with the current state of its associated wq and link it */
  static void link_pwq(struct pool_workqueue *pwq)
  {
  	struct workqueue_struct *wq = pwq->wq;
  
  	lockdep_assert_held(&wq->mutex);
  
  	/* may be called multiple times, ignore if already linked */
  	if (!list_empty(&pwq->pwqs_node))
  		return;
  
  	/*
  	 * Set the matching work_color.  This is synchronized with
  	 * wq->mutex to avoid confusing flush_workqueue().
  	 */
  	pwq->work_color = wq->work_color;
  
  	/* sync max_active to the current setting */
  	pwq_adjust_max_active(pwq);
  
  	/* link in @pwq */
  	list_add_rcu(&pwq->pwqs_node, &wq->pwqs);
  }
  
  /* obtain a pool matching @attr and create a pwq associating the pool and @wq */
  static struct pool_workqueue *alloc_unbound_pwq(struct workqueue_struct *wq,
  					const struct workqueue_attrs *attrs)
  {
  	struct worker_pool *pool;
  	struct pool_workqueue *pwq;
  
  	lockdep_assert_held(&wq_pool_mutex);
  
  	pool = get_unbound_pool(attrs);
  	if (!pool)
  		return NULL;
  
  	pwq = kmem_cache_alloc_node(pwq_cache, GFP_KERNEL, pool->node);
  	if (!pwq) {
  		put_unbound_pool(pool);
  		return NULL;
  	}
  
  	init_pwq(pwq, wq, pool);
  	return pwq;
  }
  
  /* undo alloc_unbound_pwq(), used only in the error path */
  static void free_unbound_pwq(struct pool_workqueue *pwq)
  {
  	lockdep_assert_held(&wq_pool_mutex);
  
  	if (pwq) {
  		put_unbound_pool(pwq->pool);
  		kmem_cache_free(pwq_cache, pwq);
  	}
  }
  
  /**
   * wq_calc_node_mask - calculate a wq_attrs' cpumask for the specified node
   * @attrs: the wq_attrs of interest
   * @node: the target NUMA node
   * @cpu_going_down: if >= 0, the CPU to consider as offline
   * @cpumask: outarg, the resulting cpumask
   *
   * Calculate the cpumask a workqueue with @attrs should use on @node.  If
   * @cpu_going_down is >= 0, that cpu is considered offline during
   * calculation.  The result is stored in @cpumask.
   *
   * If NUMA affinity is not enabled, @attrs->cpumask is always used.  If
   * enabled and @node has online CPUs requested by @attrs, the returned
   * cpumask is the intersection of the possible CPUs of @node and
   * @attrs->cpumask.
   *
   * The caller is responsible for ensuring that the cpumask of @node stays
   * stable.
   *
   * Return: %true if the resulting @cpumask is different from @attrs->cpumask,
   * %false if equal.
   */
  static bool wq_calc_node_cpumask(const struct workqueue_attrs *attrs, int node,
  				 int cpu_going_down, cpumask_t *cpumask)
  {
  	if (!wq_numa_enabled || attrs->no_numa)
  		goto use_dfl;
  
  	/* does @node have any online CPUs @attrs wants? */
  	cpumask_and(cpumask, cpumask_of_node(node), attrs->cpumask);
  	if (cpu_going_down >= 0)
  		cpumask_clear_cpu(cpu_going_down, cpumask);
  
  	if (cpumask_empty(cpumask))
  		goto use_dfl;
  
  	/* yeap, return possible CPUs in @node that @attrs wants */
  	cpumask_and(cpumask, attrs->cpumask, wq_numa_possible_cpumask[node]);
  	return !cpumask_equal(cpumask, attrs->cpumask);
  
  use_dfl:
  	cpumask_copy(cpumask, attrs->cpumask);
  	return false;
  }
  
  /* install @pwq into @wq's numa_pwq_tbl[] for @node and return the old pwq */
  static struct pool_workqueue *numa_pwq_tbl_install(struct workqueue_struct *wq,
  						   int node,
  						   struct pool_workqueue *pwq)
  {
  	struct pool_workqueue *old_pwq;
  
  	lockdep_assert_held(&wq->mutex);
  
  	/* link_pwq() can handle duplicate calls */
  	link_pwq(pwq);
  
  	old_pwq = rcu_access_pointer(wq->numa_pwq_tbl[node]);
  	rcu_assign_pointer(wq->numa_pwq_tbl[node], pwq);
  	return old_pwq;
  }
  
  /**
   * apply_workqueue_attrs - apply new workqueue_attrs to an unbound workqueue
   * @wq: the target workqueue
   * @attrs: the workqueue_attrs to apply, allocated with alloc_workqueue_attrs()
   *
   * Apply @attrs to an unbound workqueue @wq.  Unless disabled, on NUMA
   * machines, this function maps a separate pwq to each NUMA node with
   * possibles CPUs in @attrs->cpumask so that work items are affine to the
   * NUMA node it was issued on.  Older pwqs are released as in-flight work
   * items finish.  Note that a work item which repeatedly requeues itself
   * back-to-back will stay on its current pwq.
   *
   * Performs GFP_KERNEL allocations.
   *
   * Return: 0 on success and -errno on failure.
   */
  int apply_workqueue_attrs(struct workqueue_struct *wq,
  			  const struct workqueue_attrs *attrs)
  {
  	struct workqueue_attrs *new_attrs, *tmp_attrs;
  	struct pool_workqueue **pwq_tbl, *dfl_pwq;
  	int node, ret;
  
  	/* only unbound workqueues can change attributes */
  	if (WARN_ON(!(wq->flags & WQ_UNBOUND)))
  		return -EINVAL;
  
  	/* creating multiple pwqs breaks ordering guarantee */
  	if (WARN_ON((wq->flags & __WQ_ORDERED) && !list_empty(&wq->pwqs)))
  		return -EINVAL;
  
  	pwq_tbl = kzalloc(wq_numa_tbl_len * sizeof(pwq_tbl[0]), GFP_KERNEL);
  	new_attrs = alloc_workqueue_attrs(GFP_KERNEL);
  	tmp_attrs = alloc_workqueue_attrs(GFP_KERNEL);
  	if (!pwq_tbl || !new_attrs || !tmp_attrs)
  		goto enomem;
  
  	/* make a copy of @attrs and sanitize it */
  	copy_workqueue_attrs(new_attrs, attrs);
  	cpumask_and(new_attrs->cpumask, new_attrs->cpumask, cpu_possible_mask);
  
  	/*
  	 * We may create multiple pwqs with differing cpumasks.  Make a
  	 * copy of @new_attrs which will be modified and used to obtain
  	 * pools.
  	 */
  	copy_workqueue_attrs(tmp_attrs, new_attrs);
  
  	/*
  	 * CPUs should stay stable across pwq creations and installations.
  	 * Pin CPUs, determine the target cpumask for each node and create
  	 * pwqs accordingly.
  	 */
  	get_online_cpus();
  
  	mutex_lock(&wq_pool_mutex);
  
  	/*
  	 * If something goes wrong during CPU up/down, we'll fall back to
  	 * the default pwq covering whole @attrs->cpumask.  Always create
  	 * it even if we don't use it immediately.
  	 */
  	dfl_pwq = alloc_unbound_pwq(wq, new_attrs);
  	if (!dfl_pwq)
  		goto enomem_pwq;
  
  	for_each_node(node) {
  		if (wq_calc_node_cpumask(attrs, node, -1, tmp_attrs->cpumask)) {
  			pwq_tbl[node] = alloc_unbound_pwq(wq, tmp_attrs);
  			if (!pwq_tbl[node])
  				goto enomem_pwq;
  		} else {
  			dfl_pwq->refcnt++;
  			pwq_tbl[node] = dfl_pwq;
  		}
  	}
  
  	mutex_unlock(&wq_pool_mutex);
  
  	/* all pwqs have been created successfully, let's install'em */
  	mutex_lock(&wq->mutex);
  
  	copy_workqueue_attrs(wq->unbound_attrs, new_attrs);
  
  	/* save the previous pwq and install the new one */
  	for_each_node(node)
  		pwq_tbl[node] = numa_pwq_tbl_install(wq, node, pwq_tbl[node]);
  
  	/* @dfl_pwq might not have been used, ensure it's linked */
  	link_pwq(dfl_pwq);
  	swap(wq->dfl_pwq, dfl_pwq);
  
  	mutex_unlock(&wq->mutex);
  
  	/* put the old pwqs */
  	for_each_node(node)
  		put_pwq_unlocked(pwq_tbl[node]);
  	put_pwq_unlocked(dfl_pwq);
  
  	put_online_cpus();
  	ret = 0;
  	/* fall through */
  out_free:
  	free_workqueue_attrs(tmp_attrs);
  	free_workqueue_attrs(new_attrs);
  	kfree(pwq_tbl);
  	return ret;
  
  enomem_pwq:
  	free_unbound_pwq(dfl_pwq);
  	for_each_node(node)
  		if (pwq_tbl && pwq_tbl[node] != dfl_pwq)
  			free_unbound_pwq(pwq_tbl[node]);
  	mutex_unlock(&wq_pool_mutex);
  	put_online_cpus();
  enomem:
  	ret = -ENOMEM;
  	goto out_free;
  }
  
  /**
   * wq_update_unbound_numa - update NUMA affinity of a wq for CPU hot[un]plug
   * @wq: the target workqueue
   * @cpu: the CPU coming up or going down
   * @online: whether @cpu is coming up or going down
   *
   * This function is to be called from %CPU_DOWN_PREPARE, %CPU_ONLINE and
   * %CPU_DOWN_FAILED.  @cpu is being hot[un]plugged, update NUMA affinity of
   * @wq accordingly.
   *
   * If NUMA affinity can't be adjusted due to memory allocation failure, it
   * falls back to @wq->dfl_pwq which may not be optimal but is always
   * correct.
   *
   * Note that when the last allowed CPU of a NUMA node goes offline for a
   * workqueue with a cpumask spanning multiple nodes, the workers which were
   * already executing the work items for the workqueue will lose their CPU
   * affinity and may execute on any CPU.  This is similar to how per-cpu
   * workqueues behave on CPU_DOWN.  If a workqueue user wants strict
   * affinity, it's the user's responsibility to flush the work item from
   * CPU_DOWN_PREPARE.
   */
  static void wq_update_unbound_numa(struct workqueue_struct *wq, int cpu,
  				   bool online)
  {
  	int node = cpu_to_node(cpu);
  	int cpu_off = online ? -1 : cpu;
  	struct pool_workqueue *old_pwq = NULL, *pwq;
  	struct workqueue_attrs *target_attrs;
  	cpumask_t *cpumask;
  
  	lockdep_assert_held(&wq_pool_mutex);
  
  	if (!wq_numa_enabled || !(wq->flags & WQ_UNBOUND))
  		return;
  
  	/*
  	 * We don't wanna alloc/free wq_attrs for each wq for each CPU.
  	 * Let's use a preallocated one.  The following buf is protected by
  	 * CPU hotplug exclusion.
  	 */
  	target_attrs = wq_update_unbound_numa_attrs_buf;
  	cpumask = target_attrs->cpumask;
  
  	mutex_lock(&wq->mutex);
  	if (wq->unbound_attrs->no_numa)
  		goto out_unlock;
  
  	copy_workqueue_attrs(target_attrs, wq->unbound_attrs);
  	pwq = unbound_pwq_by_node(wq, node);
  
  	/*
  	 * Let's determine what needs to be done.  If the target cpumask is
  	 * different from wq's, we need to compare it to @pwq's and create
  	 * a new one if they don't match.  If the target cpumask equals
  	 * wq's, the default pwq should be used.
  	 */
  	if (wq_calc_node_cpumask(wq->unbound_attrs, node, cpu_off, cpumask)) {
  		if (cpumask_equal(cpumask, pwq->pool->attrs->cpumask))
  			goto out_unlock;
  	} else {
  		goto use_dfl_pwq;
  	}
  
  	mutex_unlock(&wq->mutex);
  
  	/* create a new pwq */
  	pwq = alloc_unbound_pwq(wq, target_attrs);
  	if (!pwq) {
  		pr_warn("workqueue: allocation failed while updating NUMA affinity of \"%s\"\n",
  			wq->name);
  		mutex_lock(&wq->mutex);
  		goto use_dfl_pwq;
  	}
  
  	/*
  	 * Install the new pwq.  As this function is called only from CPU
  	 * hotplug callbacks and applying a new attrs is wrapped with
  	 * get/put_online_cpus(), @wq->unbound_attrs couldn't have changed
  	 * inbetween.
  	 */
  	mutex_lock(&wq->mutex);
  	old_pwq = numa_pwq_tbl_install(wq, node, pwq);
  	goto out_unlock;
  
  use_dfl_pwq:
  	spin_lock_irq(&wq->dfl_pwq->pool->lock);
  	get_pwq(wq->dfl_pwq);
  	spin_unlock_irq(&wq->dfl_pwq->pool->lock);
  	old_pwq = numa_pwq_tbl_install(wq, node, wq->dfl_pwq);
  out_unlock:
  	mutex_unlock(&wq->mutex);
  	put_pwq_unlocked(old_pwq);
  }
  
  static int alloc_and_link_pwqs(struct workqueue_struct *wq)
  {
  	bool highpri = wq->flags & WQ_HIGHPRI;
  	int cpu, ret;
  
  	if (!(wq->flags & WQ_UNBOUND)) {
  		wq->cpu_pwqs = alloc_percpu(struct pool_workqueue);
  		if (!wq->cpu_pwqs)
  			return -ENOMEM;
  
  		for_each_possible_cpu(cpu) {
  			struct pool_workqueue *pwq =
  				per_cpu_ptr(wq->cpu_pwqs, cpu);
  			struct worker_pool *cpu_pools =
  				per_cpu(cpu_worker_pools, cpu);
  
  			init_pwq(pwq, wq, &cpu_pools[highpri]);
  
  			mutex_lock(&wq->mutex);
  			link_pwq(pwq);
  			mutex_unlock(&wq->mutex);
  		}
  		return 0;
  	} else if (wq->flags & __WQ_ORDERED) {
  		ret = apply_workqueue_attrs(wq, ordered_wq_attrs[highpri]);
  		/* there should only be single pwq for ordering guarantee */
  		WARN(!ret && (wq->pwqs.next != &wq->dfl_pwq->pwqs_node ||
  			      wq->pwqs.prev != &wq->dfl_pwq->pwqs_node),
  		     "ordering guarantee broken for workqueue %s\n", wq->name);
  		return ret;
  	} else {
  		return apply_workqueue_attrs(wq, unbound_std_wq_attrs[highpri]);
  	}
  }
  
  static int wq_clamp_max_active(int max_active, unsigned int flags,
  			       const char *name)
  {
  	int lim = flags & WQ_UNBOUND ? WQ_UNBOUND_MAX_ACTIVE : WQ_MAX_ACTIVE;
  
  	if (max_active < 1 || max_active > lim)
  		pr_warn("workqueue: max_active %d requested for %s is out of range, clamping between %d and %d\n",
  			max_active, name, 1, lim);
  
  	return clamp_val(max_active, 1, lim);
  }
  
  struct workqueue_struct *__alloc_workqueue_key(const char *fmt,
  					       unsigned int flags,
  					       int max_active,
  					       struct lock_class_key *key,
  					       const char *lock_name, ...)
  {
  	size_t tbl_size = 0;
  	va_list args;
  	struct workqueue_struct *wq;
  	struct pool_workqueue *pwq;
  
  	/* see the comment above the definition of WQ_POWER_EFFICIENT */
  	if ((flags & WQ_POWER_EFFICIENT) && wq_power_efficient)
  		flags |= WQ_UNBOUND;
  
  	/* allocate wq and format name */
  	if (flags & WQ_UNBOUND)
  		tbl_size = wq_numa_tbl_len * sizeof(wq->numa_pwq_tbl[0]);
  
  	wq = kzalloc(sizeof(*wq) + tbl_size, GFP_KERNEL);
  	if (!wq)
  		return NULL;
  
  	if (flags & WQ_UNBOUND) {
  		wq->unbound_attrs = alloc_workqueue_attrs(GFP_KERNEL);
  		if (!wq->unbound_attrs)
  			goto err_free_wq;
  	}
  
  	va_start(args, lock_name);
  	vsnprintf(wq->name, sizeof(wq->name), fmt, args);
  	va_end(args);
  
  	max_active = max_active ?: WQ_DFL_ACTIVE;
  	max_active = wq_clamp_max_active(max_active, flags, wq->name);
  
  	/* init wq */
  	wq->flags = flags;
  	wq->saved_max_active = max_active;
  	mutex_init(&wq->mutex);
  	atomic_set(&wq->nr_pwqs_to_flush, 0);
  	INIT_LIST_HEAD(&wq->pwqs);
  	INIT_LIST_HEAD(&wq->flusher_queue);
  	INIT_LIST_HEAD(&wq->flusher_overflow);
  	INIT_LIST_HEAD(&wq->maydays);
  
  	lockdep_init_map(&wq->lockdep_map, lock_name, key, 0);
  	INIT_LIST_HEAD(&wq->list);
  
  	if (alloc_and_link_pwqs(wq) < 0)
  		goto err_free_wq;
  
  	/*
  	 * Workqueues which may be used during memory reclaim should
  	 * have a rescuer to guarantee forward progress.
  	 */
  	if (flags & WQ_MEM_RECLAIM) {
  		struct worker *rescuer;
  
  		rescuer = alloc_worker();
  		if (!rescuer)
  			goto err_destroy;
  
  		rescuer->rescue_wq = wq;
  		rescuer->task = kthread_create(rescuer_thread, rescuer, "%s",
  					       wq->name);
  		if (IS_ERR(rescuer->task)) {
  			kfree(rescuer);
  			goto err_destroy;
  		}
  
  		wq->rescuer = rescuer;
  		rescuer->task->flags |= PF_NO_SETAFFINITY;
  		wake_up_process(rescuer->task);
  	}
  
  	if ((wq->flags & WQ_SYSFS) && workqueue_sysfs_register(wq))
  		goto err_destroy;
  
  	/*
  	 * wq_pool_mutex protects global freeze state and workqueues list.
  	 * Grab it, adjust max_active and add the new @wq to workqueues
  	 * list.
  	 */
  	mutex_lock(&wq_pool_mutex);
  
  	mutex_lock(&wq->mutex);
  	for_each_pwq(pwq, wq)
  		pwq_adjust_max_active(pwq);
  	mutex_unlock(&wq->mutex);
  
  	list_add(&wq->list, &workqueues);
  
  	mutex_unlock(&wq_pool_mutex);
  
  	return wq;
  
  err_free_wq:
  	free_workqueue_attrs(wq->unbound_attrs);
  	kfree(wq);
  	return NULL;
  err_destroy:
  	destroy_workqueue(wq);
  	return NULL;
  }
  EXPORT_SYMBOL_GPL(__alloc_workqueue_key);
  
  /**
   * destroy_workqueue - safely terminate a workqueue
   * @wq: target workqueue
   *
   * Safely destroy a workqueue. All work currently pending will be done first.
   */
  void destroy_workqueue(struct workqueue_struct *wq)
  {
  	struct pool_workqueue *pwq;
  	int node;
  
  	/* drain it before proceeding with destruction */
  	drain_workqueue(wq);
  
  	/* sanity checks */
  	mutex_lock(&wq->mutex);
  	for_each_pwq(pwq, wq) {
  		int i;
  
  		for (i = 0; i < WORK_NR_COLORS; i++) {
  			if (WARN_ON(pwq->nr_in_flight[i])) {
  				mutex_unlock(&wq->mutex);
  				return;
  			}
  		}
  
  		if (WARN_ON((pwq != wq->dfl_pwq) && (pwq->refcnt > 1)) ||
  		    WARN_ON(pwq->nr_active) ||
  		    WARN_ON(!list_empty(&pwq->delayed_works))) {
  			mutex_unlock(&wq->mutex);
  			return;
  		}
  	}
  	mutex_unlock(&wq->mutex);
  
  	/*
  	 * wq list is used to freeze wq, remove from list after
  	 * flushing is complete in case freeze races us.
  	 */
  	mutex_lock(&wq_pool_mutex);
  	list_del_init(&wq->list);
  	mutex_unlock(&wq_pool_mutex);
  
  	workqueue_sysfs_unregister(wq);
  
  	if (wq->rescuer) {
  		kthread_stop(wq->rescuer->task);
  		kfree(wq->rescuer);
  		wq->rescuer = NULL;
  	}
  
  	if (!(wq->flags & WQ_UNBOUND)) {
  		/*
  		 * The base ref is never dropped on per-cpu pwqs.  Directly
  		 * free the pwqs and wq.
  		 */
  		free_percpu(wq->cpu_pwqs);
  		kfree(wq);
  	} else {
  		/*
  		 * We're the sole accessor of @wq at this point.  Directly
  		 * access numa_pwq_tbl[] and dfl_pwq to put the base refs.
  		 * @wq will be freed when the last pwq is released.
  		 */
  		for_each_node(node) {
  			pwq = rcu_access_pointer(wq->numa_pwq_tbl[node]);
  			RCU_INIT_POINTER(wq->numa_pwq_tbl[node], NULL);
  			put_pwq_unlocked(pwq);
  		}
  
  		/*
  		 * Put dfl_pwq.  @wq may be freed any time after dfl_pwq is
  		 * put.  Don't access it afterwards.
  		 */
  		pwq = wq->dfl_pwq;
  		wq->dfl_pwq = NULL;
  		put_pwq_unlocked(pwq);
  	}
  }
  EXPORT_SYMBOL_GPL(destroy_workqueue);
  
  /**
   * workqueue_set_max_active - adjust max_active of a workqueue
   * @wq: target workqueue
   * @max_active: new max_active value.
   *
   * Set max_active of @wq to @max_active.
   *
   * CONTEXT:
   * Don't call from IRQ context.
   */
  void workqueue_set_max_active(struct workqueue_struct *wq, int max_active)
  {
  	struct pool_workqueue *pwq;
  
  	/* disallow meddling with max_active for ordered workqueues */
  	if (WARN_ON(wq->flags & __WQ_ORDERED))
  		return;
  
  	max_active = wq_clamp_max_active(max_active, wq->flags, wq->name);
  
  	mutex_lock(&wq->mutex);
  
  	wq->saved_max_active = max_active;
  
  	for_each_pwq(pwq, wq)
  		pwq_adjust_max_active(pwq);
  
  	mutex_unlock(&wq->mutex);
  }
  EXPORT_SYMBOL_GPL(workqueue_set_max_active);
  
  /**
   * current_is_workqueue_rescuer - is %current workqueue rescuer?
   *
   * Determine whether %current is a workqueue rescuer.  Can be used from
   * work functions to determine whether it's being run off the rescuer task.
   *
   * Return: %true if %current is a workqueue rescuer. %false otherwise.
   */
  bool current_is_workqueue_rescuer(void)
  {
  	struct worker *worker = current_wq_worker();
  
  	return worker && worker->rescue_wq;
  }
  
  /**
   * workqueue_congested - test whether a workqueue is congested
   * @cpu: CPU in question
   * @wq: target workqueue
   *
   * Test whether @wq's cpu workqueue for @cpu is congested.  There is
   * no synchronization around this function and the test result is
   * unreliable and only useful as advisory hints or for debugging.
   *
   * If @cpu is WORK_CPU_UNBOUND, the test is performed on the local CPU.
   * Note that both per-cpu and unbound workqueues may be associated with
   * multiple pool_workqueues which have separate congested states.  A
   * workqueue being congested on one CPU doesn't mean the workqueue is also
   * contested on other CPUs / NUMA nodes.
   *
   * Return:
   * %true if congested, %false otherwise.
   */
  bool workqueue_congested(int cpu, struct workqueue_struct *wq)
  {
  	struct pool_workqueue *pwq;
  	bool ret;
  
  	rcu_read_lock_sched();
  
  	if (cpu == WORK_CPU_UNBOUND)
  		cpu = smp_processor_id();
  
  	if (!(wq->flags & WQ_UNBOUND))
  		pwq = per_cpu_ptr(wq->cpu_pwqs, cpu);
  	else
  		pwq = unbound_pwq_by_node(wq, cpu_to_node(cpu));
  
  	ret = !list_empty(&pwq->delayed_works);
  	rcu_read_unlock_sched();
  
  	return ret;
  }
  EXPORT_SYMBOL_GPL(workqueue_congested);
  
  /**
   * work_busy - test whether a work is currently pending or running
   * @work: the work to be tested
   *
   * Test whether @work is currently pending or running.  There is no
   * synchronization around this function and the test result is
   * unreliable and only useful as advisory hints or for debugging.
   *
   * Return:
   * OR'd bitmask of WORK_BUSY_* bits.
   */
  unsigned int work_busy(struct work_struct *work)
  {
  	struct worker_pool *pool;
  	unsigned long flags;
  	unsigned int ret = 0;
  
  	if (work_pending(work))
  		ret |= WORK_BUSY_PENDING;
  
  	local_irq_save(flags);
  	pool = get_work_pool(work);
  	if (pool) {
  		spin_lock(&pool->lock);
  		if (find_worker_executing_work(pool, work))
  			ret |= WORK_BUSY_RUNNING;
  		spin_unlock(&pool->lock);
  	}
  	local_irq_restore(flags);
  
  	return ret;
  }
  EXPORT_SYMBOL_GPL(work_busy);
  
  /**
   * set_worker_desc - set description for the current work item
   * @fmt: printf-style format string
   * @...: arguments for the format string
   *
   * This function can be called by a running work function to describe what
   * the work item is about.  If the worker task gets dumped, this
   * information will be printed out together to help debugging.  The
   * description can be at most WORKER_DESC_LEN including the trailing '\0'.
   */
  void set_worker_desc(const char *fmt, ...)
  {
  	struct worker *worker = current_wq_worker();
  	va_list args;
  
  	if (worker) {
  		va_start(args, fmt);
  		vsnprintf(worker->desc, sizeof(worker->desc), fmt, args);
  		va_end(args);
  		worker->desc_valid = true;
  	}
  }
  
  /**
   * print_worker_info - print out worker information and description
   * @log_lvl: the log level to use when printing
   * @task: target task
   *
   * If @task is a worker and currently executing a work item, print out the
   * name of the workqueue being serviced and worker description set with
   * set_worker_desc() by the currently executing work item.
   *
   * This function can be safely called on any task as long as the
   * task_struct itself is accessible.  While safe, this function isn't
   * synchronized and may print out mixups or garbages of limited length.
   */
  void print_worker_info(const char *log_lvl, struct task_struct *task)
  {
  	work_func_t *fn = NULL;
  	char name[WQ_NAME_LEN] = { };
  	char desc[WORKER_DESC_LEN] = { };
  	struct pool_workqueue *pwq = NULL;
  	struct workqueue_struct *wq = NULL;
  	bool desc_valid = false;
  	struct worker *worker;
  
  	if (!(task->flags & PF_WQ_WORKER))
  		return;
  
  	/*
  	 * This function is called without any synchronization and @task
  	 * could be in any state.  Be careful with dereferences.
  	 */
  	worker = probe_kthread_data(task);
  
  	/*
  	 * Carefully copy the associated workqueue's workfn and name.  Keep
  	 * the original last '\0' in case the original contains garbage.
  	 */
  	probe_kernel_read(&fn, &worker->current_func, sizeof(fn));
  	probe_kernel_read(&pwq, &worker->current_pwq, sizeof(pwq));
  	probe_kernel_read(&wq, &pwq->wq, sizeof(wq));
  	probe_kernel_read(name, wq->name, sizeof(name) - 1);
  
  	/* copy worker description */
  	probe_kernel_read(&desc_valid, &worker->desc_valid, sizeof(desc_valid));
  	if (desc_valid)
  		probe_kernel_read(desc, worker->desc, sizeof(desc) - 1);
  
  	if (fn || name[0] || desc[0]) {
  		printk("%sWorkqueue: %s %pf", log_lvl, name, fn);
  		if (desc[0])
  			pr_cont(" (%s)", desc);
  		pr_cont("\n");
  	}
  }
  
  /*
   * CPU hotplug.
   *
   * There are two challenges in supporting CPU hotplug.  Firstly, there
   * are a lot of assumptions on strong associations among work, pwq and
   * pool which make migrating pending and scheduled works very
   * difficult to implement without impacting hot paths.  Secondly,
   * worker pools serve mix of short, long and very long running works making
   * blocked draining impractical.
   *
   * This is solved by allowing the pools to be disassociated from the CPU
   * running as an unbound one and allowing it to be reattached later if the
   * cpu comes back online.
   */
  
  static void wq_unbind_fn(struct work_struct *work)
  {
  	int cpu = smp_processor_id();
  	struct worker_pool *pool;
  	struct worker *worker;
  
  	for_each_cpu_worker_pool(pool, cpu) {
  		WARN_ON_ONCE(cpu != smp_processor_id());
  
  		mutex_lock(&pool->attach_mutex);
  		spin_lock_irq(&pool->lock);
  
  		/*
  		 * We've blocked all attach/detach operations. Make all workers
  		 * unbound and set DISASSOCIATED.  Before this, all workers
  		 * except for the ones which are still executing works from
  		 * before the last CPU down must be on the cpu.  After
  		 * this, they may become diasporas.
  		 */
  		for_each_pool_worker(worker, pool)
  			worker->flags |= WORKER_UNBOUND;
  
  		pool->flags |= POOL_DISASSOCIATED;
  
  		spin_unlock_irq(&pool->lock);
  		mutex_unlock(&pool->attach_mutex);
  
  		/*
  		 * Call schedule() so that we cross rq->lock and thus can
  		 * guarantee sched callbacks see the %WORKER_UNBOUND flag.
  		 * This is necessary as scheduler callbacks may be invoked
  		 * from other cpus.
  		 */
  		schedule();
  
  		/*
  		 * Sched callbacks are disabled now.  Zap nr_running.
  		 * After this, nr_running stays zero and need_more_worker()
  		 * and keep_working() are always true as long as the
  		 * worklist is not empty.  This pool now behaves as an
  		 * unbound (in terms of concurrency management) pool which
  		 * are served by workers tied to the pool.
  		 */
  		atomic_set(&pool->nr_running, 0);
  
  		/*
  		 * With concurrency management just turned off, a busy
  		 * worker blocking could lead to lengthy stalls.  Kick off
  		 * unbound chain execution of currently pending work items.
  		 */
  		spin_lock_irq(&pool->lock);
  		wake_up_worker(pool);
  		spin_unlock_irq(&pool->lock);
  	}
  }
  
  /**
   * rebind_workers - rebind all workers of a pool to the associated CPU
   * @pool: pool of interest
   *
   * @pool->cpu is coming online.  Rebind all workers to the CPU.
   */
  static void rebind_workers(struct worker_pool *pool)
  {
  	struct worker *worker;
  
  	lockdep_assert_held(&pool->attach_mutex);
  
  	/*
  	 * Restore CPU affinity of all workers.  As all idle workers should
  	 * be on the run-queue of the associated CPU before any local
  	 * wake-ups for concurrency management happen, restore CPU affinty
  	 * of all workers first and then clear UNBOUND.  As we're called
  	 * from CPU_ONLINE, the following shouldn't fail.
  	 */
  	for_each_pool_worker(worker, pool)
  		WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task,
  						  pool->attrs->cpumask) < 0);
  
  	spin_lock_irq(&pool->lock);
  
  	for_each_pool_worker(worker, pool) {
  		unsigned int worker_flags = worker->flags;
  
  		/*
  		 * A bound idle worker should actually be on the runqueue
  		 * of the associated CPU for local wake-ups targeting it to
  		 * work.  Kick all idle workers so that they migrate to the
  		 * associated CPU.  Doing this in the same loop as
  		 * replacing UNBOUND with REBOUND is safe as no worker will
  		 * be bound before @pool->lock is released.
  		 */
  		if (worker_flags & WORKER_IDLE)
  			wake_up_process(worker->task);
  
  		/*
  		 * We want to clear UNBOUND but can't directly call
  		 * worker_clr_flags() or adjust nr_running.  Atomically
  		 * replace UNBOUND with another NOT_RUNNING flag REBOUND.
  		 * @worker will clear REBOUND using worker_clr_flags() when
  		 * it initiates the next execution cycle thus restoring
  		 * concurrency management.  Note that when or whether
  		 * @worker clears REBOUND doesn't affect correctness.
  		 *
  		 * ACCESS_ONCE() is necessary because @worker->flags may be
  		 * tested without holding any lock in
  		 * wq_worker_waking_up().  Without it, NOT_RUNNING test may
  		 * fail incorrectly leading to premature concurrency
  		 * management operations.
  		 */
  		WARN_ON_ONCE(!(worker_flags & WORKER_UNBOUND));
  		worker_flags |= WORKER_REBOUND;
  		worker_flags &= ~WORKER_UNBOUND;
  		ACCESS_ONCE(worker->flags) = worker_flags;
  	}
  
  	spin_unlock_irq(&pool->lock);
  }
  
  /**
   * restore_unbound_workers_cpumask - restore cpumask of unbound workers
   * @pool: unbound pool of interest
   * @cpu: the CPU which is coming up
   *
   * An unbound pool may end up with a cpumask which doesn't have any online
   * CPUs.  When a worker of such pool get scheduled, the scheduler resets
   * its cpus_allowed.  If @cpu is in @pool's cpumask which didn't have any
   * online CPU before, cpus_allowed of all its workers should be restored.
   */
  static void restore_unbound_workers_cpumask(struct worker_pool *pool, int cpu)
  {
  	static cpumask_t cpumask;
  	struct worker *worker;
  
  	lockdep_assert_held(&pool->attach_mutex);
  
  	/* is @cpu allowed for @pool? */
  	if (!cpumask_test_cpu(cpu, pool->attrs->cpumask))
  		return;
  
  	/* is @cpu the only online CPU? */
  	cpumask_and(&cpumask, pool->attrs->cpumask, cpu_online_mask);
  	if (cpumask_weight(&cpumask) != 1)
  		return;
  
  	/* as we're called from CPU_ONLINE, the following shouldn't fail */
  	for_each_pool_worker(worker, pool)
  		WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task,
  						  pool->attrs->cpumask) < 0);
  }
  
  /*
   * Workqueues should be brought up before normal priority CPU notifiers.
   * This will be registered high priority CPU notifier.
   */
  static int workqueue_cpu_up_callback(struct notifier_block *nfb,
  					       unsigned long action,
  					       void *hcpu)
  {
  	int cpu = (unsigned long)hcpu;
  	struct worker_pool *pool;
  	struct workqueue_struct *wq;
  	int pi;
  
  	switch (action & ~CPU_TASKS_FROZEN) {
  	case CPU_UP_PREPARE:
  		for_each_cpu_worker_pool(pool, cpu) {
  			if (pool->nr_workers)
  				continue;
  			if (create_and_start_worker(pool) < 0)
  				return NOTIFY_BAD;
  		}
  		break;
  
  	case CPU_DOWN_FAILED:
  	case CPU_ONLINE:
  		mutex_lock(&wq_pool_mutex);
  
  		for_each_pool(pool, pi) {
  			mutex_lock(&pool->attach_mutex);
  
  			if (pool->cpu == cpu) {
  				spin_lock_irq(&pool->lock);
  				pool->flags &= ~POOL_DISASSOCIATED;
  				spin_unlock_irq(&pool->lock);
  
  				rebind_workers(pool);
  			} else if (pool->cpu < 0) {
  				restore_unbound_workers_cpumask(pool, cpu);
  			}
  
  			mutex_unlock(&pool->attach_mutex);
  		}
  
  		/* update NUMA affinity of unbound workqueues */
  		list_for_each_entry(wq, &workqueues, list)
  			wq_update_unbound_numa(wq, cpu, true);
  
  		mutex_unlock(&wq_pool_mutex);
  		break;
  	}
  	return NOTIFY_OK;
  }
  
  /*
   * Workqueues should be brought down after normal priority CPU notifiers.
   * This will be registered as low priority CPU notifier.
   */
  static int workqueue_cpu_down_callback(struct notifier_block *nfb,
  						 unsigned long action,
  						 void *hcpu)
  {
  	int cpu = (unsigned long)hcpu;
  	struct work_struct unbind_work;
  	struct workqueue_struct *wq;
  
  	switch (action & ~CPU_TASKS_FROZEN) {
  	case CPU_DOWN_PREPARE:
  		/* unbinding per-cpu workers should happen on the local CPU */
  		INIT_WORK_ONSTACK(&unbind_work, wq_unbind_fn);
  		queue_work_on(cpu, system_highpri_wq, &unbind_work);
  
  		/* update NUMA affinity of unbound workqueues */
  		mutex_lock(&wq_pool_mutex);
  		list_for_each_entry(wq, &workqueues, list)
  			wq_update_unbound_numa(wq, cpu, false);
  		mutex_unlock(&wq_pool_mutex);
  
  		/* wait for per-cpu unbinding to finish */
  		flush_work(&unbind_work);
  		destroy_work_on_stack(&unbind_work);
  		break;
  	}
  	return NOTIFY_OK;
  }
  
  #ifdef CONFIG_SMP
  
  struct work_for_cpu {
  	struct work_struct work;
  	long (*fn)(void *);
  	void *arg;
  	long ret;
  };
  
  static void work_for_cpu_fn(struct work_struct *work)
  {
  	struct work_for_cpu *wfc = container_of(work, struct work_for_cpu, work);
  
  	wfc->ret = wfc->fn(wfc->arg);
  }
  
  /**
   * work_on_cpu - run a function in user context on a particular cpu
   * @cpu: the cpu to run on
   * @fn: the function to run
   * @arg: the function arg
   *
   * It is up to the caller to ensure that the cpu doesn't go offline.
   * The caller must not hold any locks which would prevent @fn from completing.
   *
   * Return: The value @fn returns.
   */
  long work_on_cpu(int cpu, long (*fn)(void *), void *arg)
  {
  	struct work_for_cpu wfc = { .fn = fn, .arg = arg };
  
  	INIT_WORK_ONSTACK(&wfc.work, work_for_cpu_fn);
  	schedule_work_on(cpu, &wfc.work);
  	flush_work(&wfc.work);
  	destroy_work_on_stack(&wfc.work);
  	return wfc.ret;
  }
  EXPORT_SYMBOL_GPL(work_on_cpu);
  #endif /* CONFIG_SMP */
  
  #ifdef CONFIG_FREEZER
  
  /**
   * freeze_workqueues_begin - begin freezing workqueues
   *
   * Start freezing workqueues.  After this function returns, all freezable
   * workqueues will queue new works to their delayed_works list instead of
   * pool->worklist.
   *
   * CONTEXT:
   * Grabs and releases wq_pool_mutex, wq->mutex and pool->lock's.
   */
  void freeze_workqueues_begin(void)
  {
  	struct workqueue_struct *wq;
  	struct pool_workqueue *pwq;
  
  	mutex_lock(&wq_pool_mutex);
  
  	WARN_ON_ONCE(workqueue_freezing);
  	workqueue_freezing = true;
  
  	list_for_each_entry(wq, &workqueues, list) {
  		mutex_lock(&wq->mutex);
  		for_each_pwq(pwq, wq)
  			pwq_adjust_max_active(pwq);
  		mutex_unlock(&wq->mutex);
  	}
  
  	mutex_unlock(&wq_pool_mutex);
  }
  
  /**
   * freeze_workqueues_busy - are freezable workqueues still busy?
   *
   * Check whether freezing is complete.  This function must be called
   * between freeze_workqueues_begin() and thaw_workqueues().
   *
   * CONTEXT:
   * Grabs and releases wq_pool_mutex.
   *
   * Return:
   * %true if some freezable workqueues are still busy.  %false if freezing
   * is complete.
   */
  bool freeze_workqueues_busy(void)
  {
  	bool busy = false;
  	struct workqueue_struct *wq;
  	struct pool_workqueue *pwq;
  
  	mutex_lock(&wq_pool_mutex);
  
  	WARN_ON_ONCE(!workqueue_freezing);
  
  	list_for_each_entry(wq, &workqueues, list) {
  		if (!(wq->flags & WQ_FREEZABLE))
  			continue;
  		/*
  		 * nr_active is monotonically decreasing.  It's safe
  		 * to peek without lock.
  		 */
  		rcu_read_lock_sched();
  		for_each_pwq(pwq, wq) {
  			WARN_ON_ONCE(pwq->nr_active < 0);
  			if (pwq->nr_active) {
  				busy = true;
  				rcu_read_unlock_sched();
  				goto out_unlock;
  			}
  		}
  		rcu_read_unlock_sched();
  	}
  out_unlock:
  	mutex_unlock(&wq_pool_mutex);
  	return busy;
  }
  
  /**
   * thaw_workqueues - thaw workqueues
   *
   * Thaw workqueues.  Normal queueing is restored and all collected
   * frozen works are transferred to their respective pool worklists.
   *
   * CONTEXT:
   * Grabs and releases wq_pool_mutex, wq->mutex and pool->lock's.
   */
  void thaw_workqueues(void)
  {
  	struct workqueue_struct *wq;
  	struct pool_workqueue *pwq;
  
  	mutex_lock(&wq_pool_mutex);
  
  	if (!workqueue_freezing)
  		goto out_unlock;
  
  	workqueue_freezing = false;
  
  	/* restore max_active and repopulate worklist */
  	list_for_each_entry(wq, &workqueues, list) {
  		mutex_lock(&wq->mutex);
  		for_each_pwq(pwq, wq)
  			pwq_adjust_max_active(pwq);
  		mutex_unlock(&wq->mutex);
  	}
  
  out_unlock:
  	mutex_unlock(&wq_pool_mutex);
  }
  #endif /* CONFIG_FREEZER */
  
  static void __init wq_numa_init(void)
  {
  	cpumask_var_t *tbl;
  	int node, cpu;
  
  	/* determine NUMA pwq table len - highest node id + 1 */
  	for_each_node(node)
  		wq_numa_tbl_len = max(wq_numa_tbl_len, node + 1);
  
  	if (num_possible_nodes() <= 1)
  		return;
  
  	if (wq_disable_numa) {
  		pr_info("workqueue: NUMA affinity support disabled\n");
  		return;
  	}
  
  	wq_update_unbound_numa_attrs_buf = alloc_workqueue_attrs(GFP_KERNEL);
  	BUG_ON(!wq_update_unbound_numa_attrs_buf);
  
  	/*
  	 * We want masks of possible CPUs of each node which isn't readily
  	 * available.  Build one from cpu_to_node() which should have been
  	 * fully initialized by now.
  	 */
  	tbl = kzalloc(wq_numa_tbl_len * sizeof(tbl[0]), GFP_KERNEL);
  	BUG_ON(!tbl);
  
  	for_each_node(node)
  		BUG_ON(!zalloc_cpumask_var_node(&tbl[node], GFP_KERNEL,
  				node_online(node) ? node : NUMA_NO_NODE));
  
  	for_each_possible_cpu(cpu) {
  		node = cpu_to_node(cpu);
  		if (WARN_ON(node == NUMA_NO_NODE)) {
  			pr_warn("workqueue: NUMA node mapping not available for cpu%d, disabling NUMA support\n", cpu);
  			/* happens iff arch is bonkers, let's just proceed */
  			return;
  		}
  		cpumask_set_cpu(cpu, tbl[node]);
  	}
  
  	wq_numa_possible_cpumask = tbl;
  	wq_numa_enabled = true;
  }
  
  static int __init init_workqueues(void)
  {
  	int std_nice[NR_STD_WORKER_POOLS] = { 0, HIGHPRI_NICE_LEVEL };
  	int i, cpu;
  
  	WARN_ON(__alignof__(struct pool_workqueue) < __alignof__(long long));
  
  	pwq_cache = KMEM_CACHE(pool_workqueue, SLAB_PANIC);
  
  	cpu_notifier(workqueue_cpu_up_callback, CPU_PRI_WORKQUEUE_UP);
  	hotcpu_notifier(workqueue_cpu_down_callback, CPU_PRI_WORKQUEUE_DOWN);
  
  	wq_numa_init();
  
  	/* initialize CPU pools */
  	for_each_possible_cpu(cpu) {
  		struct worker_pool *pool;
  
  		i = 0;
  		for_each_cpu_worker_pool(pool, cpu) {
  			BUG_ON(init_worker_pool(pool));
  			pool->cpu = cpu;
  			cpumask_copy(pool->attrs->cpumask, cpumask_of(cpu));
  			pool->attrs->nice = std_nice[i++];
  			pool->node = cpu_to_node(cpu);
  
  			/* alloc pool ID */
  			mutex_lock(&wq_pool_mutex);
  			BUG_ON(worker_pool_assign_id(pool));
  			mutex_unlock(&wq_pool_mutex);
  		}
  	}
  
  	/* create the initial worker */
  	for_each_online_cpu(cpu) {
  		struct worker_pool *pool;
  
  		for_each_cpu_worker_pool(pool, cpu) {
  			pool->flags &= ~POOL_DISASSOCIATED;
  			BUG_ON(create_and_start_worker(pool) < 0);
  		}
  	}
  
  	/* create default unbound and ordered wq attrs */
  	for (i = 0; i < NR_STD_WORKER_POOLS; i++) {
  		struct workqueue_attrs *attrs;
  
  		BUG_ON(!(attrs = alloc_workqueue_attrs(GFP_KERNEL)));
  		attrs->nice = std_nice[i];
  		unbound_std_wq_attrs[i] = attrs;
  
  		/*
  		 * An ordered wq should have only one pwq as ordering is
  		 * guaranteed by max_active which is enforced by pwqs.
  		 * Turn off NUMA so that dfl_pwq is used for all nodes.
  		 */
  		BUG_ON(!(attrs = alloc_workqueue_attrs(GFP_KERNEL)));
  		attrs->nice = std_nice[i];
  		attrs->no_numa = true;
  		ordered_wq_attrs[i] = attrs;
  	}
  
  	system_wq = alloc_workqueue("events", 0, 0);
  	system_highpri_wq = alloc_workqueue("events_highpri", WQ_HIGHPRI, 0);
  	system_long_wq = alloc_workqueue("events_long", 0, 0);
  	system_unbound_wq = alloc_workqueue("events_unbound", WQ_UNBOUND,
  					    WQ_UNBOUND_MAX_ACTIVE);
  	system_freezable_wq = alloc_workqueue("events_freezable",
  					      WQ_FREEZABLE, 0);
  	system_power_efficient_wq = alloc_workqueue("events_power_efficient",
  					      WQ_POWER_EFFICIENT, 0);
  	system_freezable_power_efficient_wq = alloc_workqueue("events_freezable_power_efficient",
  					      WQ_FREEZABLE | WQ_POWER_EFFICIENT,
  					      0);
  	BUG_ON(!system_wq || !system_highpri_wq || !system_long_wq ||
  	       !system_unbound_wq || !system_freezable_wq ||
  	       !system_power_efficient_wq ||
  	       !system_freezable_power_efficient_wq);
  	return 0;
  }
  early_initcall(init_workqueues);
  